282 PALEOZOIC PALEONTOLOGY. 
and sinus, which do not extend beyond the middle of the shell, and 
usually by a single median plication in the fold and sinus. In the 
younger individuals, before the plications begin to be developed, the 
surface is entirely smooth. 
The dimensions of a full-grown individual are: length, 5.5 mm.; 
width, 5.5 mm.; thickness, 3.5 mm. 
Remarks.—This little species resembles younger individuals of R. 
altiplicata, but may always be distinguished by the smooth posterior 
portion of the shell, the plications ending at about the middle, while 
in FR. altiplicata they reach nearly to the beak. 
RHYNCHONELLA ALTIPLICATA Hall. 
Plate XXIX., Figs. 24-27. 
1859. Rhynchonella altiplicata Hall, Pal. N. Y., vol. IIL, p. 231, pl. 
33, figs. 2 a-k. 
Description.—Shell broader than long, subtriangular or broadly 
subovate in outline. Pedicle valve with a pointed, incurved beak, 
depressed anteriorly in a deep, angular sinus, which extends to the 
umbo and bears a single, strong, angular, median plication. Brachial 
valve more convex than the pedicle, elevated in front in an angular 
mesial fold. Both valves marked by three or four simple, angular 
plications on each side of the fold and sinus, which continue nearly 
to the beak, and with a single median plication on the fold and sinus. 
The dimensions of a large specimen are: length, 8.5 mm.; width, 
10.5 mm.; thickness, 6.5 mm. 
Remarks.—This species, as described in the New York Paleontology, 
is typically a member of the fauna of the New Scotland beds, but in 
New Jersey the shell so identified occurs in the Coeymans limestone, 
where it rarely grows as large as in New York. Usually the shell does 
not attain a greater length than 6 mm., but occasionally an individual 
is observed fully as large as the New York representatives. It re- 
sembles the associated R. semiplicata, and sometimes seems to grade 
into that species, but typically it is proportionally broader and is 
marked by plications which reach much nearer to the beak. 
