-]Yeller — Kinderhook Faunal Studies. 81 



stone of Cooper County, Missouri, and as Swallow's name 

 has priority it is here adopted. It is possible that both these 

 names should be considered as synonymous with R. lineata 

 (Martin), but this can be certainly determined only when a 

 large number of specimens can be compared. These sand- 

 stone specimens are, of course, all casts and consequently the 

 surface markings of the shells are indistinct, the concentric 

 lines usually being the only ones that can be definitely 

 recognized. 



BRYOZOA. 



Impressions of bryozoa belonging to Fenestella or some 

 allied genus are not uncommon in the Chonopectus sandstone, 

 but the state of their preservation is not such as to admit of 

 their identification. 



MOIiLUSCA. 



PELECYPODA. 



AVICULOPECTEN TENUICOSTUS Win. 

 PI. III. f, 3. 



" Shell small, equilateral ; pallial margin circularly rounded 

 between anterior and posterior extremities, which lie midway 

 between the beak and the opposite side. Beak shghtly promi- 

 nent ; body of shell bounded by a truncation from beak to 

 each lateral margin; anterior truncation slightly concave. 

 Anterior wing of left valve moderately inflated, as long as 

 anterior side of shell, distinctly rounded at extremity, joining 

 hinge-line by a rounded angle, and separated from body of 

 shell by a broadly V-shaped sinus, rounded at the bottom. 

 Posterior wing only very imperfectly seen. Surface (of left 

 valve) ornamented by fine, rigid, nearly equidistant ribs, 50 

 or 60 in number, separated by concave intervals ; similar but 

 finer ribs or striae marking the anterior ear. Frequently 

 from three to five equidistant costate elevations appear, each 

 of which bears two or three of the ribs. A few inequidistant 

 concentric lines are seen. Right valve unknown." 



Remarks. The types of this species consist of seven 



