522 Systematic Paleontology 



Genus PERISSONOTA Conrad 

 [Am. Jour. Conch., 1869, vol. v, p. 98] 



Type. — Perissonota protexta Conrad. 



" Equivalved, elongated ; posterior hinge line long, curved, linear, with 

 numerous close, transverse teeth, extending nearly to the end margin ; 

 anterior hinge area broad, oblique and somewhat distant from the hinge 

 margin. No fosset under the apex ? " — Conrad, 1869. 



The characters which isolate the group are the anterior umbones, the 

 marked posterior extension of the shell, and the persistence of the posterior 

 dental series almost to the extremity of the dorsal margin. The pallial 

 sinus is unknown, but it is quite probable that the species referred to this 

 group will find their proper station as a subgenus under Yoldia. 



A. Posterior dorsal margin not approximately parallel to the base line, 



external surface regularly striated concentrically. . .Perissonota protexta 



B. Posterior dorsal margin approximately parallel to the base line; exter- 



nal surface not regularly striated concentrically Perissonota littlii 



Perissonata protexta Conrad 



Perrisonota protexta Conrad, 1869, Am. Jour. Conch., vol. v, p. 98, pi. ix, 



fig. 24. 

 Perrisonota protexta Whitfield, 1885, Mon. U. S. Geol. Survey, vol. ix, p. 110, 



pi. xi, figs. 14, 15. 

 Leda protexta Johnson, 1905, Proc. Acad. Nat. Sci., Phila., p. 8. 

 Perrisonota protexta Weller, 1907, Geol. Survey of New Jersey, Pal., vol. iv, 



p. 379, pi. xxx, figs. 1, 2. 



Description. — " Subensiform, smooth, convex; anterior side short, 

 extremity situated nearer the hinge than ventral margin." — Conrad, 1869. 



Type Locality. — Haddonfield, New Jersey. 



" Shell small, ensiform, extremely elongated posteriorly, and gradually 

 narrowed from the beaks. Valves depressed convex with very small incon- 

 spicuous beaks, which curved backward, and with an obsolete carination 

 extending from them backward to the postero-basal angle. Anterior end 

 broadest, sharply rounded ; posterior end narrowly rounded, longest above 

 the middle. Hinge line arched upward in front of the beaks, and gently 

 concave posteriorly throughout the entire length of the shell. Basal line 



Etymology: Perissonota, from 7rep«r<r6s, beyond, and j/cDtos, back; an allu- 

 sion to the abnormal extension of the teeth along the dorsal region. 



