Retrorsirostra carleyi

• Easily distinguished by the outward slant of the interarea of the pedicle valve
• Biconvex strophic brachiopod
• Plano-convex geometry
• Coarsely costate ornamentation
• Procline orientation of the interarea relative to the commisural plane

• Compared with Plaesiomys, Retrorsirostra appears to have a thin-walled shell posterior and delicate internal structure, such as reduced dental plates and brachiophore supports, probably as a result of the formation of a procline ventral interarea and drastic reduction in the ventral umbo. The aditicules and epipunctae are well developed, identical to those of (the Anticosti Island, Canada brachiopod) Plaesiomys anticostiensis in size, density, and arrangement on the shell structure.

Davis (1998):

• Articulate brachiopod. This species is easily distinguished by the outward slant of the interarea of the pedicle valve. Limited to a thin zone in the Arnheim.

Copper (1996):

• The procline orthide Retrosirostra carleyi, from the Upper Ordovician Richmond Group of Ohio shows well preserved canals lining the interareas and the valve floor posterior to the gonocoeles (Figure 1:3-4), thus confirming the proposal that the disposition of mantle along the hinge region in the orthides generally is as previously described for the clitambonitidines.

Alexander (1983):

• Biconvex strophic brachiopod
• Plano-convex geometry
• Coarsely costate ornamentation
• Procline orientation of the interarea relative to the commisural plane
• Length of the anterior-posterior axis may (nearly) equal maximum valve width

Richards (1972):

• Retrorsirostra carleyi, the sole member of the third orthid morphological group, is a convexo-concave costellate orthid of medium to large size, with large individuals attaining a width of 45 mm. It is unique among Richmondian orthids in possessing a strongly concave pedicle valve, the interarea of which is procline. The pedicle opening is large at all stages of development, suggesting the presence of a stout pedicle.
• R. carleyi occurs in abundance in a narrow zone low in the Tanner’s Creek Formation, where it is associated with Rafinesquina alternata in a deposit of shell gravel and shale.

Hall (1860):

• Shell transversely subelliptical or subquadrate, resupinate; hinge-line less than the greatest width of the shell, usually from two-thirds to three-fourths as long; extremely compressed towards the cardinal extremeties, and the angles rounded; font margin often subtruncate; sides nearly straight, or more or less rounded. Dorsal valve gibbous, acuate and incurved at the umbo, and flattened in the middle towards the front; area narrow. Ventral valve flattened near the cardinal angles, elevated and obtusely pointed at the beak, towards the front: beak straight, the plane of the area inclined forwards; area large, triangular, with a large open foramen which reaches the beak. Surface strongly striate, the margin of each valve being marked by from fifty to seventy rounded or subangular striae. Some of the striae are simple and continuous from the beack, the increase taking place chiefly by implantation; while a small number are bifurcate. The length of the shells of this species is sometimes an inch and a quarter or more.

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