230 Bulletin 39 403 



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

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

 t}'; 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 posteriori}^; 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 Lophocardiuni , 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 v/as described by Dr. Maurj^ from the Gur- 

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

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

 ical Lophocardium and representing the first member of this in- 

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

 men is ver}^ fragmentar}^, 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 closel}^ the 

 L. A7i7iettce 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. Cufningi Brod- 

 erip, the tj-pe 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. 



