1894. PROCEEDINGS OF THE NATIONAL MUSEUM. 99 



discriminated from the latter by tlie presence of a deep thonjib small 

 ]»allial sinns and a long, arched, posterior lateral tooth. 



(tNATHODON CLATHRODON, C'ourud (euiended). 



Plate VII, tig. 9. 



Mactnt daihrodonlu, Conrad, Am. Journ. Sci., 1st ser., xxiii, p. 340, 1833. 

 (inathodon (jraiji, Conijad, Medial Tert., -p. 23, pi. 13, fig. 1, 1838; Ibid., second ed. 



by Dali, 1893.— Emmons, Geol. Rep. N. Car., p. 298, tig. 226a, 1858. 

 Gnathodon minor, Conhad, Medial Tert., p. 69, pi. 39, tig. 6, May, 1840 (Testa 



.junior). Am. Jouru. Sci., 1st ser., xu, p. 347, pi. 2, lig. 14, Oct., 1841. 



Not of Whittield. 

 lianr/ia minor, Conuad, Proc. Acad. Nat. 8ci. Phila., xii, p. 232, 1861. 

 Bam/ia clathrodonla, Conrad, oj}. cit., xir, p. 2.32, 1861. — Prime, Proc. Bost. Soc. 



N. Hist., VII, p. 347, 1861. 

 Iian<jia {Perissodon) cJathrodonta, Conrad, Proc. Acad. Nat. Sci. for 1862, p. 573, 



1863.— Meek, Smithsonian Misc. Coll. 183, Checkl. Inv. Fos. Mioc. N. Am., 



p. 11, 1864. 

 Kanf/ia (Perissodon) minor, Conrad, Proc. Acad. Nat. Sci.. Phila. for 1862, p. 573, 



1863.— Meek, Checklist, p. 11, 1864. 



Chesapeake Miocene of James and York rivers, Virginia and IS^orth 

 Carolina, Conrad, Ruffin, nnd Yarrow; Pliocene of the Croatau beds 

 in North Carolina, Jolinson. 



The dimensions of an adnlt specimen are: Length, 70; height, 54.5; 

 diameter, 40 mm. 



This is the oldcvst species of the genus, and appears in the Chesa- 

 peake Miocene of Virginia, but seems to l)e very limited in its distri- 

 bution. I have seen no specimens from south of North Carolina. It 

 may be discriminated from O. cuncatus by its thinner and more com- 

 pressed shell, its slender and straighter lateral teeth, its more shallow 

 and open cartilage ])it, its less prominent and more adjacent beaks. The 

 pallial sinus is small but angular. The lateral teeth are crenulate, 

 especially above; the posterior end of the shell, though not rostrate, is 

 rather pointed. 



A subgenus Perissodon proposed for this sjtccies by Conrad, but 

 never defined, seems to have been based on the specific differences 

 above referred to. There are certainly no features of more than spe- 

 cific value separating this form from G. cuneatus. 1 am quite confident 

 that Conrad's G. minor j described from the same beds as G. elathrodon, 

 is merely a young stage of the latter. Conrad's figure agrees with such 

 young shells very well, and his descrii)tion afibrds no differential 

 characters. 



