292 
PALAEONTOLOGY OF NEW-YORK. 
347. 4. AVICULA DEMISSA. 
Pl. LXXX. Figs. 2 a, b. 
Avicula demissa. Cokhad, Jour. Acad. Nat. Sciences, 1S42, Vol. viii, pag. 243, pi. 13, fig. 3. 
—• — Emmons, Geol. Report, 1842, pag. 404, fig. 2. 
Obliquely subovate, compressed, extended posteriorly into a broad triangular wing ; 
anterior wing short, obtuse ; surface marked by close, sharp, imbricating, lamellose strise ; 
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 striae, which are crowded 
together on the posterior wing, and at its junction with the body of the shell. The shell 
presents some variations in form, but preserves the sharp striae in all the specimens seen. 
Fig. 2 a. 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'? DESQUAMATA. 
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. Conbad, Ann. Geol. Report, 183S, p. 114; 1839, p. 63. 
— — Vanuxem, Geol. Report, pag. 65, fig. 1. 
— — Emmons, Geol. Report, pag. 402, fig. 1. 
Compare Pterinea carinata , Goldfttss, Vol. ii, pag. 136, tab. 119, fig. 8. 
Equivalve, obliquely obovate, extending into acute curving beaks; anterior slope nearly 
straight above, and rounded below ; posterior slope oblique, scarcely alate ; surface marked 
