230 



Bulletin 39 



margin; the anterior end is well rounded into the base; the pos- 

 terior end is more contracted and gaping slightly at its extremi- 

 ty; surface sculpture on the body of the shell, anteriorly con- 

 sists of narrow, concentric wrinkles which are best developed on 

 the anterior end but become obsolete on the middle of the shell 

 and posteriorly; in addition the whole surface carries fine, 

 sub-obsolete radial threads; on the posterior area, the sculpture 

 is of heavier and coarser radial threads, lacking the concentric, 

 except the irregular growth lines. 



Height 56, length 32, diameter 20 mm. 



The subgenus Lophocardiiini , of which there are two recent 

 species along the West Coast of Mexico, differs from the true 

 Protocardia, in its gaping posterior end and lack of lateral teeth 

 as well-as in important difference in its anatomical structure. 

 The shells are strongly convex, with high, inflated umbos and 

 are extremily thin and fragile. 



The P. gurabica was described by Dr. Maury from the Gur- 

 abo formation of Santo Domingo, and compared by her with the 

 Vickburgian P. diver sa Conrad, but it appears to me to be a typ- 

 ical Lofyhocardiiim and representing the first member of this in- 

 teresting subgenus to be found in the fossil state. As her speci- 

 men is very fragmentary, I have redescribed the species from 

 better preserved Panama and Costa Rican material. The poster- 

 ior end is gaping and the internal mold shows no impression of 

 lateral teeth along the hinge margin. It approaches closely the 

 L. AmiettcB Dall, dredged from 8 to 27 fathoms in the Gulf of 

 California, except that it is proportionately longer and lacks the 

 concentric wrinkles on its posterior area. The L. Cumingi Brod- 

 erip, the type of the subgenus, carries between its posterior area 

 and the general surface of the shell, a thin radial lamina or crest, 

 extending from the umbos to the ventral margin. 



The fossil shell is extremily thin. It generally occurs simp- 

 ly as internal molds which may still retains a part of the shell 

 or impression of its sculpture on its surface. 



