346 
PALEONTOLOGY* OP NEW-YORK. 
Rliyiielionclla venustula. 
PLATE LY. 
Atrypa cuboides : Vanuxem (non Sowerby), Geol. Report Third Dist. New-York, p. 163, f. 1. 
«« « ? Hail, Geol. Report Fourth Dist. New-York, p. 215 and 216, f. 1. 
Compare Atrypa cuboides : Sowerby, Geol. Transactions, 2d series, Yol.v, pl.lvi, f. 23. 
Also “ << Philips, Palaeozoic Fossils of Cornwall and Devon, pa. 85, pi. xxxiv 
f. 150. • 
Also Texebratula crenulata : Id. ib. p. 85, f. 152. 
Also Atrypa subcuboides, D’Orbiqny = A. cuboides, Philips (non Sowerby), Prodrome, Yol. i, 
p. 93, n.884. 
Shell in the young state oval or ovate, with a moderate or scarcely per¬ 
ceptible sinus, and few or no plications except upon the middle of the 
shell; becoming gibbous, rotund or subcuboid, with the width a little 
greater than the length, and the depth from two-thirds to three-fourths 
as great as the length, with a deep sinus and the surface entirely pli¬ 
cated ; cardinal line extending for two-thirds or three-fourths the 
width of the shell. 
Ventral valve in young shells a little less convex than the dorsal, and 
moderately or scarcely at all depressed in the sinus. In older shells 
the ventral valve is moderately convex in the middle above, and 
abruptly depressed in the broad deep sinus, while it is flat or concave 
towards the lateral margins. Umbo moderately elevated, with the 
beak minute and closely appressed. The cardinal margins are often so 
abruptly incurved as to give the appearance of a narrow area on each 
side of the apex. 
Dorsal valve in young shells a little more gibbous than the opposite, 
and without defined mesial elevation; becoming more gibbous with 
the growth of the shell. In full-grown specimens the dorsal valve is 
very gibbous, with a defined mesial fold reaching above the middle 
of the shell, sharply truncate in front, and usually bearing six or seven 
plicaations; the sides of the shell curve very abruptly and almost ver¬ 
tically to the opposite valve. The apex is very abruptly incurved 
beneath the beak of the opposite valve. 
Surface in young shells marked by about four plications in the mesial 
sinus; while there are from ten to fifteen on the sides of the shell, 
