OF CONCHOLOGY. 97 



polished ; anterior and posterior margins nearly equally oblique ; 

 extremities acutely and nearly equally rounded ; beaks not pro- 

 minent or inclined. 



Locality. — Tippah Co.? Miss. 



NEMODON, Conrad. 



Description. Equivalved, thin ; hinge line long and straight, 

 or slightly curved under the umbo ; hinge in the left valve with 

 three linear teeth parallel with the anterior cardinal margin ; 

 posterior lateral tooth double, very long, linear ; under the apex 

 a few granular teeth. 



N. EuFALENSis, Conrad. — PI. 9, fig. 16. 



Description. Trapezoidal, elongated, thin, contracted from 

 umbo to base; summit obtuse ; concentric lines minute and punc- 

 tate ; radiating lines very minute and indistinct; posterior mar- 

 gin oblique, slightly rounded. 



Area i^Macrodon) Eufalensis, Gabb. 



Locality. Haddonfield, N. J. 



This genus is related to the older Macrodon, Lycett, and to 

 the Eocene Area ketei'odonta, which Deshayes places in a group 

 of 3 species, under the name CuculJaries. I think these 3 spe- 

 cies are not representatives of one genus, but of three. Macro- 

 don characterizes the Jurassic era, NemodoJi the Cretaceous, and 

 O^icidlaria, as represented by Ay-ca heterodon, Deshayes, the 

 older Eocene. 



Area heterodon, Desh., is a species of this genus, which is ex- 

 clusively Cretaceous. 



NEMOARCA, Conrad. 

 N. CRETACEA, Conrad. — PI. 9, fig. 21. 



Description. — Trapezoidal, short, ventricose, subequilateral ; 

 ribs 30 as far as umbonal slope, linear, except 3 or 4 nearest to 

 the umbonal slope, which are wider, and one of them grooved ; 

 ribs on the anterior submargin and post umbonal area close and 

 minute ; hinge line linear, teeth minute, oblique. 



Locality. Haddonfield, N. J. 



This small species more nearly resembles Striarca, Conrad, 

 than any other Cretaceous bivalve ; but it has the cardinal teeth 

 oblique. There is no internal plate, and the radiating lines are 

 more prominent than in Trigonarca. No species of this genus 

 has been found in the Eocene or later Tertiaries. 



