OF CONCHOLOGY. 77 



dulated slightly and having four thick concentric ribs and nu- 

 merous prominent lines ; inner margin crenulated. 



Locality. — South Carolina. Cast, in the phosphate deposits. 

 Miocene 'i 



These casts are so well defined that the hinge and external 

 character of the shell can readily be studied by making moulds 

 in wax or plaster. 



The ventricose disks, which are common in the hard or cohe- 

 rent phosphate rock, usually show a somewhat undulated sur- 

 face. The generic character pei'fectly agrees with that of the 

 preceding. Venus Lamarckii is a recent species of this genus. 



DOSINIA, Scopoli. 

 D. OBOVATA, Conrad. 



Dione obovata, Conrad, Mioc. Foss. 14, 8, 4. 



YENUS. 



V. (Circumphalos) alveata, Say, figured in Say's American 

 Conch, is probably V. (C.) athleta, Con., not alveata, Conrad. 



Univalves, 



DENTALIUM ? 



? D. hamatus. Under a lens this cast shows a minute, very 

 closely granulated surface, slightly iridescent. This also appears 

 on a fragment of the inner part of the shell. This character, 

 together with the expanded base, renders it doubtful whether 

 this shell belongs to the family Dentaliidce. I propose to name 

 it Falcula. 



D. hamatus, Conrad, Amer. Journ. Conch, vol. v, p. 44, pi. 

 1, figs. 12, 16. 



CREPIDULA Lam. 

 C. ROSTRATA, Conrad. 



Description. — Thin, inflated, umbo very narrow and promi- 

 nent, beak incurved, pointed above the margin of aperture ; 

 diaphragm short, margin slightly concave. 



Locality. — Virginia. JNIiocene. 



Allied to C. cymha^formis, Conrad, but may be distinguished 

 by its thin substance, narrow umbo and incurved apex ; while 

 the umbo cavity is solid in the former species, in this it is open 

 to the apex, and the margin of the inner plate is not sinuous as 

 in the former. 



