Mesotrypa patella

• Lenticular Zoarium
• 25 mm. average width, though can be up to 38 mm.
• Smooth surface, slightly hirsute from acanthopore projections
• Clusters of cells larger than average, but not above a normal range
• Circular to polygonal apertures, normally around 0.19 mm. but up to 0.25 mm.
• Each Zooecium is touched by four others with an acanthopore situated at or near the contact points
• Mesopores in interspaces

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Brown & Daly (1985):

• Diagnosis: Zoaria encrusting, thin, small, with small thin-walled zooecia diaphragms common throughout, numerous mesozooecia, and numerous large acanthopores.
• Description: Zooecia with short recumbent part at base, quickly bending upward and rising straight and direct to surface. Intermonticular zooecia typically subovate to subcircular, rarely subpolygonal, moderately small (8+ in 2 mm, 0.2 mm MZD; table 18), long, typically erect and of uniform size throughout thin zoaria and generally with curved sides. Virtually all zooecia in close contact along sides.
  Zooecial walls thin (0.01 mm ZWT), straight from basal area to surface, and of indefinite structure.
  Diaphragms thin, commonly straight and horizontal, less commonly inclined or curved, rarely cystoid, and spaced about one-half to one zooecial tube diameter apart, though some areas having them absent for some distance. Many diaphragms seem to bend into walls but untraceable into wall structure. ]
  Mesozooecia numerous (19+ M1M), typically triangular in shape with curved walls at almost every wall angle where they conspicuously separate zooecia; a few mesozooecia rectangular to elongate. Many arising just above recumbent basal part of colony and extending for some distance before pinching out or passing from plane of section; some extending to surface. Other mesozooecia arising within zoarium and some continuing to surface. Mesozooecia conspicuously more closely tabulate than zooecia.
  Acanthopores numerous (20 A1M) and large (0.06 mm MAD), with a large lumen, rising from basal area along wall angles and continuing for long distances, a few to the surface. Zooecia conspicuously and typically surrounded by three acanthopores slightly inflecting into the apertures. Acanthopores composed of long laminae concentrically arranged about a prominent translucent core. Monticules not recognized.
• Discussion: Utgaard and Perry 91964, p. 69) discussed the salient points of similarity between their Whitewater specimens of M. patella and Ulrich’s holotype. Our specimens from lower in the section agree well in most structural characters, including zooecia in 2 mm, mesopores in 1 sq mm, acanthopores in 1 sq mm, and average acanthopore diameter. Our specimens, however, have some acanthopores of slightly larger diameter, fewer curved or cystoid diaphragms, and diaphragms locally remote or absent. We consider that these differences are within the range of growth variability.
  M. pauca Utgaard and Perry has much fewer mesozooecia and smaller and more numerous acanthopores than M. patella. The former also has thicker walls.
  M. spinosa Ulrich from Middle Ordovician strata in Minnesota and Kentucky is similar in many respects to M. patella. The former species, however, has slightly fewer zooecia in 2 mm, smaller and fewer acanthopores, and many fewer diaphragms that are more typically inclined or curved than M. patella.

James (1894): Under original name Diplotrypa patella

• Corallum lenticular, 25 to 38 mm. in diameter and 2 to 4 mm. thick at the center; surface smooth, the spiniform corallites projecting above the edges of the calices; clusters of cells slightly larger than the average, but not elevated above the general level; under surface with a thin and concentrically wrinkled epitheca; corallites thin-walled, eight in two mm., calices circular or polygonal, normal ones .18mm., but larger ones .25 mm. in diameter, arranged in diagonally intersecting series; interspaces occupied by spiniform corallites; tabulae moderately abundant; straight or curved, especially in the lower part of the tube; tabulae more numerous in the small than in the large corallites.

Ulrich (1890): Under original name Diplotrypa patella

• Zoarium lenticular; the typical specimen is twenty-five mm. across, another larger example thirty-eight mm. across; greatest thickness, at centre, from two to four mm. Surface smooth, thinly hirsute from the surface projections of the acanthopores, showing clusters of cells larger than the average, but not elevated above the general level. Under surface provided with a thin and somewhat concentrically wrinkled epitheca. Zooecia very thin walled, about eight to two mm. Apertures circular, sometimes polygonal, those of the normal size about 0.19 mm., the larger 0.25 mm. in diameter, arranged in diagonally intersecting series. Usually, each zooecium is touched by four others, with an acanthopore situated at or very near the point of contact. The interspaces between the zooecia are occupied by mesopores, bounded by three or four concave sides, mesopores more numerous in the slusters of larger cells. In the zooecial tubes, diaphragms are moderately abundant, straight, at times curved, especially in the lower part of the tubes where they frequently have the appearance of cystiphargms and may actually be of that nature. In the mesopores the diaphragms are closely set, about three in the space of a tube diameter.

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