292 PALEONTOLOGY OF NEW-YORK. 



347. 4. AVICULA DEMISSA. 



Pl. LXXX. Figs. 2 a, b. 



Avicvla demisfa. Cois-rap, Jour. Acad. Nat. Sciences, 1S42, Vol. viii, pag. 243, pl. 13, fig. 3. 

 — Emmons, Geol. Report, 1S42, pag. 404, fig. 2. 



Obliquely suiiovate, compressed, extended posteriorly into a broad triangular wing ; 

 anterior wing short, obtuse ; surface marked by close, sharp, imbricating, lamellose striae ; 

 posterior wing extending beyond the line of the posterior extremity of the shell ; anterior 

 and posterior margins nearly parallel, and but slightly oblique. 



This species is characterized by the sharp elevated concentric strias, which arc crowded 

 together on the posterior wing, and at its jimction with the body of the shell. The shell 

 presents some variations in form, bnt preserves the sharp striee in all the specimens seen. 



Fig. 2 n. A large perfect specimen, which is more elevated than usual. 

 Fig. 2 b. The impression of a smaller specimen in sandstone. 



Position and locality. This species is found in the higher part of the Hudson-river group, 

 near Rome, Oneida county, and at Pulaski. It likewise occurs in the same position in Ohio. 

 Rolled fragments of the calcareous portions of the group, containing this shell, are 

 frequently found on the south shore of Lake Ontario. (State Collection ) 



348. 5. AVICULA 1 DESQUAJWATA. 



Pl. LXXX. Figs. 3 a, b. 



Suborbicular, convex in the middle ; beak nearly central ; hinge line slightly extended 

 on each side ; surface scaly, or with elevated imbricating lamellae, which desquamate, 

 giving the surface a rough scaly appearance. 



The characters of this species are not clearly decided, though it appears referable to the 

 Genus Avicula. 



Fig. 3 a. A specimen, natural size. 3 b. An enlarged portion of the surface. 



Position and locality. This species has been found only in the calcareous beds associated 

 with the shales of the Hudson-river group, near Troy. 



349. 7. AMBONYCHIA RADIATA. 



Pl. LXXX. Figs. 4a-/. 



Pterinea carinata. Conhad, Ann. Geol. Report, IS3S, p. 114; 1839, p. H.3. 



— — Vanuxem, Geol. Report, pag. Ci5, fig. 1. 



— — F.MMONs, Geol. Report, pag. 402, fig. 1. 

 Compare Pterinea carinata, Goldfuss, Vol. ii, pag. 13(5, tab. 119, fig. S. 



Equivalve, obliquely obovate, extending into acute curving beaks ; anterior slope nearly 

 straight above, and rounded below ; posterior slope oblique, scarcely alate ; surface marked 



