PALEONTOLOGY. 451 



Genus NYASSA H. & W. 



Preliminary Notice of Lamellibranchiata shells of the Upper Helderberg Hamilton 

 and Chemung Groups, etc., Albany, N. Y. 1869, p. 28 (generic description 

 omitted) :— Whitf. Ann. N. Y. Acad. Sci., 1882, p. 216. 



Shells bivalve, very oblique and transversely ovate in form. Posterior hinge- 

 plate narrow, bearing from one to four long, slender, ridge-like teeth. Anterior 

 plate broad, marked by numerous small point-like teeth with intermediate depres- 

 sions, arranged somewhat radiating from the middle of its inner border. Adductor 

 muscles two, one at each extremity. Pallial line entire. Ligament internal. Type, 

 JV. arguta. Name, mythological. Geological range, so far as known, Devonian. 

 Family relations apparently near Megalomus Hall, and Megalodon Sowerby. 



Nyassa arguta. 



Plate; VII, fig. 18. 

 Nyassa arguta H. and W. Prelim. Notice of the Lamellib. Shells of the Upper 

 Held., Hamilton and Chemung Groups, etc., Albany, N. Y., Dec. 1869, p. 28; — 

 Whitf., Ann. N. Y. Acad. Sci., 1882, p. 216. 



Shell of medium size, transversely sub-ovate or sub-trapezodial, much longer 

 than high. Valves moderately ventricose, most prominent along the umbonal ridge, 

 which is stronly arcuate and sub-angular. Beaks rather small and appressed, slightly 

 incurved, and situated near the anterior end. Surface of the valve generally de- 

 clining from the umbonal ridge to the basal line, and with a slight sinus or sulcus 

 below the ridge, which gradually widens toward the margin of the shell, where it 

 causes a broad, but not marked, emargination in the border of the shell. Cardinal 

 slcpe narrow and abrupt; hinge-line arcuate; posterior end of the shell narrowed; 

 anterior end broad, rounded, and slightly excavated below the beaks. 



Surface of the shell marked by concentric lines of growth parallel to the mar- 

 gin of the valve, and often forming rather strong, irregular varices, most distinctly 

 marked on the anterior half of the shell. 



The Ohio specimens, although preserved in an entirely different 

 matrix, are yet such exact counterparts of the New York shells that no 

 question can exist of their positive identity. 



Formation and Locality. — In limestone above the "Bone-bed" in 

 Tully township, Marion County, Ohio. The specimen figured is from 

 the State Cabinet at the State University, Columbus, Ohio. 



Genus GRAMMYSIA DeVern. 

 Grammysia bisnlcata. 



Plate VII, fig. 19. 

 Pholadomya ano'nala Goldf. Pet. Germanica, p. 272, pi. 157, fig. 9. 

 Pterinea bisuicata Conrad, Ann. Rept. Geol. Surv. N. Y., 1838, p. 16. 

 Cypricardites bisculcata Conrad, Ann. Rept. Geol. Surv. N. Y., 1841, p.' 52. 

 Grammysia Hamiltonensis DeVern., Bui. Geol. Soc, France, 2d Series, vol. 4, p. 696, 



1847. 

 Cardinia Hamiltonensis DeOrb., Prod. Palseou., vol. 1, p. 76, 1850. 

 Grammysia bisculcata Conrad, H. and W. Prelim. Notice Lamellib. Shell of the Up. 



Held. Hamilton and Chemung Groups. Published as ext. from Rept. State 



Cab., Dec. 1869. (Anonymously.) 



