CHEMUNG GROUP. 
263 
1. Avicula pecteniformis, n. s.—Plano-convex; upper valve flat, surface (except the wings) 
plain or with fine concentric striae ; posterior wing with strong elevated radiating ribs ; an¬ 
terior wing acute, with a fold ; lower valve slightly convex, surface and posterior wing marked 
by strong radii or ribs of unequal size, which become obsolete or undulating toward the margin; 
anterior wing with a single strong fold, and finer radii; posterior wing large, and extending 
into an obtuse angle beyond the margin of the shell. 
The flat plain upper valve, and the unequal ribs which become obsolete toward the margin 
of the lower valve, are distinguishing characters of this shell. 
Localities —Chemung narrows ; Cayuta creek. 
3. Avicula longispina, n. s. — Obliquely subovate or elliptical, convex; surface marked 
by concentric lines ; beak prominent, extending above the hinge line ; anterior margin scarcely 
produced into a wing, but slightly extended in a curve beyond a deep fold ; posterior wing 
very small, and suddenly extended into a long spine. 
From the convexity of the shell, the wing and spine are usually covered, which may lead 
to mistaking the fossil. It is not uncommon. 
Localities —Painted-post; Jasper ; Cassadaga lake. 
4. Avicula spinigera (Conrad, Jour. Acad. Nat. Sci., Vol. 8, p. 237, pi. 12, fig. 3).— 
Obliquely subovate, with concentric lines and wrinkles ; anterior wing short, obtuse ; posterior 
wing small, suddenly produced into a long slender spine. 
The spine is often broken off in removing the rock from around the shell, but some portion 
of it can always be seen. In this species the spine is less parallel to the direction of the 
shell, which is also smaller than No. 3 ; both often occurring together. 
Localities —Painted-post; Jasper; Chemung. 
& 
2. Avicula acanthoptera. 
1, a and b. Avicula Damnoniensis. (Sowerby in Geol. Trans., New series, vol. 5, pi. 53, 
fig. 22. Phillips, Palceozoic Fossils, pi. 23, figs. 90, 91, 92.) — Fig. 1 is the usual form; 
a, a shorter variety ; and b, a specimen compressed so that the wing is scarcely perceptible. 
In these specimens, which are from the soft green shale of Steuben county, the longitudinal 
striations are not visible ; though in specimens from other localities, they are distinct. 
118. 
1, a and 6. Avicula Damnoniensis. 
