16 



bonil ridge aumilai- aud extending to tlie post- basal extremity. 

 Valves somewhat tlattoued below the umboues and bearing au unde- 

 fined shallow suleus that becoaics obsolete before reaching the basal 

 margin. Post-cardinal slope flattened. Surface of the casts marked by 

 faint concentric lines. We have four specimens belonging to this spe- 

 cies, all of them are casts, aud each one is broken at some point, 

 but together, they show the entire valves. No part of the shell 

 is preserved, aud no muscular scars can be distinguished. 



Wiiile this species has little resemblance to any other one in 

 this genus, we have little doubt that it is a true CypricdrdeUa. 



Found by R. A. Blair, in the Chouteau limestone, at Sedalia, 

 Missouri, and now in the collection of S. A. Miller. 



Family ORTHONOTID.i:. 



PAL.?;OSOLEN OCCIDENTALIS, n. Sp. 



Philc 11, Fiij. ]■'!, cdrdbuil view; Ft;/. 14, left vdlve of same 

 specimen, ilie posferior purl -is broken nway. 



Species quite as large or larger than the type of the genus. 

 Shell solenoid but the true length unknown. From other frag- 

 ments than the one illustrated it is inferred that it represents 

 only the anterior half and that the length is five times the height, 

 but it may be only four times the height. Shell subcylindrical, 

 basal and cardinal margins subparallel. Anterior end obtusely 

 pointed. Posterior end unknown. Beaks near the anterior end, 

 low, but curved over the cardinal line. Umbones rounded and 

 fade away into the general convexity of the shell. Muscular im- 

 pressi(3n large, round and anterior to the beaks. Ligament evi- 

 dently external. Pallial lino not observed. Hinge teeth, if any, 

 unknown. Surface marked with distant concentric lines of growth 

 which are crossed by a few, distant, radiating lines shown upon 

 the cast. The shell, itself, is not preserved. 



Tin's species is readily distinguished from P. siliqxtoideiis, the 

 only other known species, by the general outline and surface 

 characters, and yet, we think they are congeneric. The muscular 

 impression is nnknown in P. siliiiuoidemt, but it must be quite 

 Hmiill, while, in this speciep, it ii very large. /*. sili<iuoideiis 

 hIiows no evidence of an external hinge ligament, and Hall said 

 that it was, probably, iuternal; but this s[)ecies, wi^ think, dearly 

 had an external ligament. 



Found by II. A. Blair, in the Chouteau liuKistone, near Sedalia, 

 ]\iiH8ouri, and now in the collection of S. A. Miller. 



