Pycnocrinus dyeri

Classification
Phylum: Echinodermata
Class: Crinoidea
Order: Monobathrida
Family: Glyptocrinidae
Genus: Pycnocrinus
Species: Pycnocrinus dyeri (Meek, 1872)

G_dyeri_paleoeco

Taxonomic Details

Formerly assigned to the genus Glyptocrinus

Stratigraphic Occurrences

Glyptocrinus_dyeri_strat

Geographic Occurrences

		
Map point data provided by iDigBio.

Stratigraphic Description

Sequences (Formations)

  • C3 (Corryville)

Identification in Hand Sample

  • Bowl shaped calyx below secondary radials, which number 12-15
  • No tertiary or intertertiary areas, and the arms bifurcate and become free at the top of the vault.
  • Strong ridge arises from the second secondary radial, passing upward across the interradial plates
  • Azygous area similar to that of G. decadactylus

P. dyeri from the Richmond Group of Cincinnati, Ohio (MUGM 28342)

Published Description

Holland (2013):

  • Twenty arms on semi-globular calyx with stellate plates.

Fossil Crinoids (1999):

  • Pycnocrinus dyeri has a distally coiled stem that was used as an attachment around bryozoans or other erect crinoid stems. The column is composed of circular columnals with nodals separated by varying numbers of internodals. The calyx has a high bowl shape and is distinguished by a median ridge along each ray and a star-shaped ridge pattern on interradial plates. The second primibrachial is axillary, but the fixed brachials do not divide again. The arms become free after six or seven secundibrachials, and after another three or four free secundibrachials, the arms divide again. Fixed pinnules are incorporated into the interradial areas, and the free arms are biserial with long, delicate pinnules.

Fossils of Ohio (1996):

  • The calyx of Pycnocrinus dyeri has plates of subequal size both in the rays and in the interradial areas. Stellate ridges characterize all calyx plates, and the circlet of radial plates is not interrupted int eh posterior. Free arms branch and have uniserial brachials. Columnals are circular. This species typically has been assigned to the genus Glyptocrinus (for example, see Davis, 1985). However, because this species has 10 free arms that branch once immediately after the arms become free, it is more properly assigned to Pycnocrinus.

James (1897):

  • Body globular, sub-turbinate, wider than high, with sides rounding under the base; under-basals obsolete, or if present not exposed externally; basals very small and projecting as a thin rim below, much wider than high, and trigonal in general outline, with the lateral angles minutely truncated; first radials of moderate size, heptagonal, wider than long; second and third a little smaller, the second being hexagonal and the third pentagonal, and supporting on its superior sloping sides the first divisions of the rows; secondary radials 8 to 11 in number, rapidly diminishing in length upward to the second bifurcation or commencement of the arms just below where a few of the smaller pieces seem to be free and bear pinnules on their inner sides; further down the second and fourth secondary radials of each ray give off, alternately on each side, small divisions that do not become free, giving rise to pinnules at the summit of the body; anal area a little wider than the interradial areas; first anal plate of about the same size as the first radials, hexagonal, and supporting in the next range 3 pieces arranged with the middle one higher than the others; while above these 3 smaller pieces can be seen arranged in the same way in the third range and 3 to 4 or 5 in the fourth; the middle plates of this series form a direct vertical row that has a rather prominent mesial, rounded ridge extending all the way up from the middle of the lowest pieces of about the same size as those passing up the primary and secondary radial series, while the other plates on each side and other parts of the lowest pieces are ornamented with radiating costae of smaller size, like those of the interradial pieces; interradial areas, not excavated below, but becoming moderately concave above; first interradial pieces about the size of the second primary radials, hexagonal, and supporting 2 other smaller pieces in the next range, that bear between their superior sloping sides a fourth smaller piece; while above this there are two pieces in the next range that connect with the pieces of the little lateral division of the secondary radials, and perhaps some other small intercalated pieces, filing the upper part of the interradial areas; auxiliary areas flat, and each occupied by an hexagonal or heptagonal piece about the size of the second piece of each secondary radial, while the space above is occupied by several much smaller pieces; arms 20, 4 to each ray, rounded on the dorsal side, slender, of moderate length, very gradually tapering, simple, and composed of very short, slightly wedge-form pieces, each of which bears a pinnule at its inner lateral end; pinnules slender, rather closely arranged, deeply furrowed on the inner side and apparently composed of rather long joints; surface of the body plates all ornamented with distinct radiating costae, starting from the center of each piece, and passing, one to each of its sides, so as to connect with others on each contiguous piece; of these costae those passing up the middle of each of the radial series are a little larger and more prominent than those of the interradial plates, while they bifurcate with the rays so as to send a division up each of the secondary radial series, toward the upper part of which they become more prominent and rounded, being those about the size of the free arms.

Meek (1871):

  • Body globular-subturbinate, being wider than high, with sides rounding under to the base. Sub-basal pieces obsolete, or, if present, not exposed externally. Basal pieces (subradials of some) very small, and projecting as a thin rim below, much wider than high, and presenting a trigonal general outline, though the lateral angles are doubtless minutely truncated. First radial pieces of moderate size, heptagonal in form, and wider than long; second and third a little smaller, the second being hexagonal, and the third pentagonal, and supporting on its superior sloping sides the first division of rays. Secondary radial or supraradial series each composed of from eight to eleven pieces, rapidly diminishing in length upward to the second bifurcation or commencement of the arms, just below which a few of the smaller pieces seem to be free and bear pinnulae on their inner sides; farther down, the second and fourth secondary radials of each ray give off, alternately on each side, small divisions that do not become free, but are soldered into the interradial walls, though they can be traced to the summit of the body, where they merely give origin to pinnules.
  • Anal area a little wider than the interradial areas. First anal plate of about the same size as the first radials, hexagonal in form, and supporting in the next range three pieces, arranged with the middle one higher than the others; while, above these, three smaller pieces can be seen arranged in the same way in the third range, and three to four or five in the fourth, which is as far up as they can be traced. The middle plates of this series form a direct vertical row, that have a rather prominent mesial, rounded ridge extending all the way up from the middle of the lowest piece, of about the same size as those passing up the primary and secondary radial series, while the other plates on each side and other parts of the lowest pieces are ornamented with radiating costae of smaller size, like those on the interradial pieces.
  • Interradial areas not excavated below, but becoming moderately concave above; first interradial pieces of about the size of the second primary radials, hexagonal in form, and supporting two other somewhat smaller pieces in the next range, that bear between their superior sloping sides a fourth smaller piece, while above these there are two pieces in the next range that connect with the pieces of the little lateral divisions of the secondary radials, and perhaps some other small intercalated pieces filling the upper part of the interradial areas.
  • Axillary areas flat, and each occupied below by a hexagonal or heptagonal piece of about the size of the second piece of each secondary radial, while the space above is occupied by several much smaller pieces.
  • Arms four to each ray, rounded on the dorsal sides, slender, of moderate length, very gradually tapering, simple, and composed of very short, slightly wedge-formed pieces, each of which bears a pinnule at its larger inner lateral end; pinnules slender, rather closely arranged, deeply furrowed on the inner side, and apparently composed of rather long joints.
  • Surface of body plates all ornamented with distinct radiating costae, starting from the centre of each piece, and passing one to each of its sides so as to connect with others on each contiguous piece: of these costee, those passing up the middle of each of the radial series are a little larger and more prominent than those of the interradial plates, while they bifurcate with the rays so as to send a division up each of the secondary radial series, toward the upper part of which they become more prominent and rounded, being there of about the size of the free arms. Column unknown. Height of body, 0.60 inch; breadth, about 0.68 inch; length of arms, 1.05 inch; thickness of same, 0.05 inch; number of joints, in a space of 0.10 inch near the base, eight.
  • This very beautiful species reminds one, by its sculpturing, of the common typical species G. decadactylus, from which, however, it may be at once distinguished by its proportionally broader and shorter body, with sides rounding regularly under to the column instead of being obconical. It also has proportionally more slender arms, and differs materially in having, in each secondary radial series, from nine to eleven pieces between the first bifurcation of each ray and the arm bases, instead of only two. In the form of its body, it agrees more nearly with G. ornatus of Billings; but it differs materially from that species in having twenty arms in- stead of only ten, as well as in less important details.
  • The specific name is given in honor of Mr. C. B. Dyer, of Cin- cinnati, Ohio, to whom I am indebted for the use of the very fine specimens from which the description was made out.
    Locality and position.-Cincinnati group of the Lower Silurian, 100 feet below tops of hills at Cincinnati, Ohio.

Miller (1883):

  • G. dyeri is distinguished from G. decadactylus by having a bowl-shaped calyx below the secondary radials, and rather less prominent ridges; by having 12 to 15 by 10 secondary radials, instead of 2 by 10, and consequently increased number of intersecondary plates; the interradial and intersecondary radial areas are not so much depressed; there are no tertiary or intertertiary areas; the arms bifurcate and become free at the top of the vault. Prof. Meek said, the second and fourth secondary radial give off alternately on each side small divisions, that do not become free, but are soldered into the interradial walls, though they can be traced to the summit of the body, where they merely give origin to pinnules.” This was a mistake. Quite a strong ridge arises from the second secondary radial, and passes upward across the interradial plates, gradually diminishing in size and disappearing at the plates of the vault; a similar, smaller ridge arises from the fourth secondary radial, and passes upward across the interradial area. These ridges appear to have been supports to the interradial areas, as the central ridge in the wider azygous area seems to have been a support to it, but they are not soldered into the interradial walls any more than the ridges that ornament the surface of the plates, and produce the sculptured appearance of the calyx are soldered to the walls; nor do they support arms, or pinnules. The azygous areas in the two species are similar, and the arms in this one are a little more delicate than in G. decadactylus. The two species agree in the general characters of the column, basals, primary radials, and number of arms; but differ materially in the region of the secondary radials, though the number of secondary radials and tertiaries, forming part of the calyx in G. decadactylus, will nearly correspond with the number of secondary radials, forming part of the calyx in G. dyeri. It occurs in the middle part of the Hudson River Group, above G. decadactylus