CHEMUNG GROUP. 
267 
5 a, b, c. Strophomena interstrialis (Orthis interstrialis and Leptoena interstrialis, Phil¬ 
lips, Palaeozoic Fossils, pages 61 and 216, pi. 25, fig. 103). — Semicircular; lower valve 
convex, upper one flat or slightly concave ; surface marked by sharp radiating striae, which 
are sometimes continuous to the margin, and at others interrupted or divaricating; between 
each pair of these striae are four or five others, much finer, and slightly undulating. 
5, is the inner side of the flat valve from Chemung. 
5 a. A magnified portion of the shell. 
5 b. The two valves, somewhat compressed, from Ithaca. 
5 c. The convex valve, with the shell partially removed, from near Elmira. 
The S. inequistriata and S. mucronata {Jour. Acad. Nat. Sci., Vol. 8, p. 254 and 257, 
pi. 14, figs. 2 & 10), appear to be identical with this shell of Mr. Phillips, and since his name 
has precedence, it is retained. It is readily known from the character of its larger and finer 
striae, in which it resembles the S. sericea and S. transversalis, from both of which it is quite 
distinct. 
It is one of the most widely distributed fossils in the group, and has a somewhat different 
aspect in the shales, sandstones and calcareous layers. 
121 . 
1 and 1 a. Orthis carinata. 2. Orthis impressa. 3 and 4. Orthis interlineata. 5. Orthis unguiculus. 
1. Orthis carinata, n. s. — Semicircular ; lower valve very convex, with a depression ex¬ 
tending from beak to base ; surface covered with fine radiating striae ; upper valve flat, with 
a sharp ridge along the centre, which is very prominent in the cast; cast of the subrostral 
impression very prominent and acute at the beak, and not deeply indented below. 
1, lower valve ; 1 a, upper valve. 
This character of the cast of the upper valve is always sufficient to distinguish the shell, 
and it is usually the most obvious character. 
Localities —Painted-post; Chemung; Jasper, in brown sandstone. 
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