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PALAEONTOLOGY OP NEW-YORK. 
resemblance to B. primipilaris or implexa. It is never abundant, and is often found 
in a crushed and distorted condition. 
Geological formations and localities. In the Hamilton group, at Moscow, York, 
Geneseo and elsewhere in Western New-York; also in the Marcellus shale at 
Avon and other places. 
Rliynclionella (Stenocisma) sappho. 
PLATE LIY. 
Rhynchonella sappho : Hail, Thirteenth Report on the State Cabinet, p. 87. 1860. 
Shell, in full-grown individuals, transverse, gibbous, subelliptical. Young 
shells broadly subtrigonal, becoming short-ovate; nearly straight in 
the middle of the front, abruptly pointed at the beak : cardinal slopes 
concave; sides rounded to the mesial fold and sinus. 
Ventral valve flabelliform, depressed-convex, rarely a little gibbous on 
the umbo, flattened and depressed in the middle towards the front; 
the sinus becoming perceptible about the middle of the length : sides 
nearly flat; apex abruptly acute, and more or less incurved according 
to age. 
Dorsal valve gibbous, regularly arching transversely; the mesial fold 
becoming conspicuous only towards the front : in young shells only 
moderately convex. 
Surface marked by twenty to twenty-two or twenty-four plications 
(fourteen or fifteen in the young shells), those towards the cardinal* 
margin less elevated; about four to six mark the sinus and fold. In 
old shells, the plications are grooved towards the front; and those of 
the sides of the dorsal valve are very abruptly bent towards the ven¬ 
tral valve, with a shorter and wider groove, and all deeply bifid for the 
reception of the opposite plication. The shell is concentrically marked 
by fine thread-like elevated strise, which are more conspicuous and 
strongly undulating towards the front of the shell, their remains being 
often preserved in the casts. 
Length and width, in full-grown shells, as seven to eight. 
