Acidaspis cincinnatiensis

Phylum: Arthropoda
Class: Trilobita
Order: Lichida
Family: Odontopleuridae
Genus: Acidaspis
Species: Acidaspis cincinnatiensis (Meek,1873)

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Includes: Acidaspis anchoralis (Miller, 1875), Ceratocephala ceralepta (Anthony, 1838) (also referred to as Acidaspis ceralepta), and Acidaspis onealli (Miller, 1875).

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Stratigraphic Occurrences


Geographic Occurrences

Map point data provided by iDigBio.
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Sequences (Formations)

  • C5 Sequence (Waynesville)
  • C3 Sequence (Mt. Auburn, Corryville)
  • C2 Sequence (Bellevue, Fairview: Fairmount, Mount Hope)
  • C1 Sequence (McMicken, Southgate, Economy/Fulton)

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Identification in Hand Sample

  • Thorax with ten segments.
  • First and second glabellar furrows deep.
  • Body subcircular in outline.
  • Length of pygidium, exclusive of spines, 0.19 inch; breadth 0.55 inch.
  • Two pairs of small border spines between major spines on the pygidium.
  • Large spines project from occipital ring of the cranidium.

Acidapsis cincinnatiensis from McMillan formation of Hamilton County, Ohio (CMCIP 54415)

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Whittington (1956):

  • Cephalon differs from that of Acidaspis brightii in that the first and second glabellar furrows are deeper, and third glabellar lobes are distinctly outlined by their convexity and by shallow third furrows. Frontal glabellar lobe projects only slightly in front of third lateral lobes. Median part of occipital ring more elevated and backwardly extended, separated by shallow median part of occipital furrow from median glabellar lobe. Occipital spine long, length (sag.) equal to, or greater than, length (sag.) of remainder of cephalon. Both branches of the suture elevated on sutural ridges (Pl. 58, figs. 9-11), the posterior merging into inflated base of librigenal spine. The spines along the lateral border are less steeply inclined, and are distally thickened and bent postero-laterally. Hypostome (P1. 59, fig. 3) preserved, slightly displaced, in a specimen, exposed from the ventral side, which probably came from the McMillan formation. The incomplete thorax is disjointed and displaced from the cephalon, but this displacement enabled the occipital ring and basal part of the large median spine to be exposed without having to destroy the thorax (Pl. 59, figs. 3,6). Width across shoulders of hypostome 3.25 mm., length (sag.) 2.3 mm. Middle body gently convex, subcircular in outline, middle furrow runs backward and slightly inward from ovate depression in antero-lateral corner; posterior lobe crescentic, with inflated tips.
  • Lateral and posterior borders of similar width; small, dorsally directed anterior wings; deep lateral notch; inflated shoulder situated at half length. Rostrum preserved in this specimen, a short (sag.), wide, plate, edge at hypostomal suture flattened, straight (except distally where it curves to meet inner edge of cheek doublure), and fits against straight, flat edge of hypostome. In this position tip of anterior wing lies immediately beneath junction of axial, pre-glabellar and third lateral glabellar furrows at antero-lateral corner of glabella, but no anterior boss is developed. The fit of the beveled edges at the hypostomal suture suggests that the hypostome lies approximately in the horizontal plane, on the orientation adopted here. Thorax of 10 segments (Pl. 59, fig. 1), in which specimen the most anterior segment is almost concealed beneath the posterior cephalic border), axis less than half width between fulcra. Pleurae divided by furrow into convex anterior band, and much more convex and wider (exs.) posterior band. Narrow (exs.) posterior flange. Posterior pleural band curves slightly backward distally, and is inflated at fulcrum, and extended into posterior pleural spine. Short, curved, blade-like anterior pleural spine (Pl. 59, fig. 6). First segment with posterior pleural spine short and beveled to fit beneath border of cephalon. Pygidium nearly three times as wide as long. First axial ring convex, second much lower, third faint. Gently raised border to pleural regions, seven pairs border spines. Fifth are major pair, slightly upwardly directed, and connected by prominent ridge to first axial ring. External surface finely granulate, except in deep furrows. Tubercles scattered on inflated parts of cephalon, middle body of hypostome, paired on axial rings of thorax and pygidium, two or three large tubercles on posterior pleural bands, row small tubercles on anterior band

Meek (1873):

  • Pygidium, exclusive of its spines, about three times as wide as long and approaching a sub-semi-circular outline, its anterior margin being straight all the way across, and about one-third of its posterior margin in the middle transversely truncated, while on each side of this the posterior lateral margins are straight to the anterior lateral angles; mesial lobe prominent at the anterior end, where it is about as wide as each lateral lobe, but, becoming rapidly depressed and narrowed posteriorly, composed of only two well-defined segments; lateral lobes flat excepting ridge that extends obliquely backward and outward from the anterior segment of the mesial lobe, across each, to the posterior margins, where these ridges terminate in prominent rounded diverging spines, while the posterior lateral margins between these and the lateral angles are each armed with four smaller spines directed obliquely backward and outward. Four similar also occupy the truncated middle parts of the posterior margin the two larger ones; surface smooth, excepting a few very minute, scattering asperities on the spines.
  • The pleurae of the posterior thoracic segment are smooth, and each a strong mesial ridge extending straight outward to the extremity, where it curves abruptly backward and is produced into a long, sharp, spine extending as far backward as the longest spines of the pygidium, or farther. Length of pygidium, exclusive of spines, 0.19 inch; breadth 0.55 inch. Transverse diameter of first thoracic segment in advance of 0.70 inch, length of each pleurae 0.23 inch, anterio- posterior of the same 0.08 inch, length of larger lateral spine of each 0.38 inch. Fragments of this species are found at all elevations from low watermark to the top of the hills back of the city but they are most abundant in the lower 200 feet of the rocks. The specimen belonging to Dr. Hill was found in the marl in Eden Park, less than 200 feet above low water mark.

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