78 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



edges of valve flattened to form narrow lateral pseudointerarea as 

 bearing for overlap of edge of brachial valve (some species without 

 overlap). 



Brachial valve strongly convex transversely, moderately convex 

 longitudinally; beak short, rounded, slightly attenuate in some, apex 

 normally within pedicle valve. 



Pedicle valve interior with one small hinge tooth on each side of 

 anterior edge of delthyrium, each parallel to valve edge ; dental plates 

 large, curved toward floor of valve, meeting above floor, there joining 

 to form low, thick median septum, thus producing deep, scoop-shaped 

 spondylium duplex; septum becoming thinner and slightly higher 

 anteriorly, extending forward about one-third length of valve. 



Brachial valve interior with short undivided hinge plate ; crura ex- 

 tending from anterior edge of hinge plate, curved gently dorsally for 

 most of length, slightly more strongly curved near anterior ends ; me- 

 dian septum beginning at beak, under hinge plate, ventral edge ex- 

 panded to form spoon-shaped camarophorium, not attached to hinge 

 plate, and without intercamarophorial plate, height increasing ante- 

 riorly, camarophorium extending slightly farther anteriorly than 

 septum, length of septum only about one-fourth length of valve on 

 floor, remaining as median keel along underside of camarophorium. 



Type species. — Psilocamara renfroarum Cooper, 1956a, Journ. Pale- 

 ontology, vol. 30, No. 3, p. 524, pi. 61B, figs. 20-32, text-fig. IB, Nos. 

 4-15 (by original designation). 



Range. — The known range of the genus at present is confined to that 

 of the type species ; Middle Pennsylvanian (Des Moines) of Texas and 

 Missouri. If Levicamera athyriformis Grabau is found to belong to 

 Psilocamara, the range of the genus will extend into the Lower Per- 

 mian in Nantan and Yunnan, China. 



Comparisons. — Psilocamara is characterized by its normally smooth 

 shell with a single high fold in the anterior margin that takes up 

 nearly the entire brachial valve and thus produces no flexture between 

 it and the flanks. Internally it is characterized by a septum in the pedi- 

 cle valve so low in the beak area that the spondylium is sessile in many 

 specimens, and by a camarophorium in the brachial valve that lacks an 

 intercamarophorial plate and is completely independent of the hinge 

 plate. The partly sessile spondylium is similar to that in species of 

 Atribonium n. gen. and Sedenticellula Cooper, but Psilocamara is 

 easily distinguished by its noncostate shell with high fold. Lack of an 

 intercamarophorial plate is a characteristic of Camarophorinella Licha- 

 rev, but Psilocamara has the edges of the camarophorium free of the 

 hinge plate, and its shell is essentially smooth. 



Camarophorina Licharev is similarly smooth, but differs from Psilo- 



