MACTRIDiE 41 



Genus, GNATHODON.— Gray. 



GNATHODON CUNEATUS. 



Plate VII. Fig. 10. 



• Gnathodon cuneatus, Gray, Sowerby Gen.,, fig. 83. 

 Rangia cyrenoides, Desmoulins. 



Gnathodon Grayii, Con., Foss. Ter. Form., p. 23, pi. 13, fig. 1. 

 Gnathodon Grayii, Tuomeij <$f Holmes, Pleiocene Foss. So. Ca., p. 99. 

 Gnathodon minor, Con., Sill. Am. Jour. Sci., Vol. 42, pi. 2, fig. 14. 



Description. Shell ovate, ventricose, inequilateral, thick; buccal margin obtusely 

 rounded, anal margin produced, angular, cuneiform ; umbones produced, prominent, eroded ; 

 epidermis olive-brown ; margin of valves acute, simple ; pallial sinus, short, ovate, outline 

 commencing near the middle of the inferior muscular impression; hinge-teeth two in each 

 valve, anterior to the cartilage-pit, which is central, deep, and ovate ; excavation extending 

 under dorsal margin nearly to the beaks ; the front tooth of the left valve angular, bifurca- 

 ted, large, beautifully crenulated externally, and at the base within that of the right valve, 

 triangular, massive, and crenulated on the outside only; the hind tooth in both valves 

 small and simple, that of the right is cleft deeply to receive the tooth of left valve ; lateral 

 teeth one in each valve, elongated, slightly curved ; anterior ends dilated ; dorsal' sides 

 beautifully crenulated ; a narrow elongated ridge resembling a tooth, and crenulated on 

 the inferior side of the anterior end, extends parallel to the lateral tooth on the dorsal side 

 of the right valve. 



Gnathodon cuneatus, is a variable shell; specimens corresponding to the various 

 descriptions given of the synonyms above named, may be had from the Post-Pleiocene 

 beds of South-Carolina; I therefore do not hesitate to refer them all to one species. 



Those from the Pleiocene have their representative in the Post-Pleiocene as well as the 

 recent forms from the Gulf coast ; and it would be as easy to make a half dozen species as 

 two or three; for example, that of the Post-Pleiocene, from which the figure in our plate 

 is taken, differs not only in form and size, but the pallial sinus is ovate, short, and transverse, 

 whilst that of the recent is angular or sub-lanceolate, and ascending. Shell beds of the 

 Post-Pleiocene like those found on the surface at Mobile and in Southern Alabama, 

 composed entirely of this species, and referred to the recent period by Professor Tuomey,* 

 underlie the city of Charleston, about sixteen feet below the surface. 



It is no longer an inhabitant of the bays of South-Carolina, but common on the Northern 

 marshes of the Gulf of Mexico. 



Plate VII. Fig. 10. 



Locality. Charleston. Museum, College of Charleston; Cabinet F. S. H. 



11 * Tuomey's Geology of Alabama, just published. 



