484 
PALAEONTOLOGY OF NEW-YORK. 
Genus Riiynchospira (Hall). 
[ Gr. pvyxog, rostrum ; oneipa, spira ; in allusion to its similarity in form to ItiiYNCHO- 
NELLA, and having internal spires.] 
Terebratula and Rhynchonella of authors. 
JValdheimia : Hall, 1856. 
Trematospira, Subgenus Jthynchospira : Hall, 1857. 
Jthynchospira : Hall, 1858. 
Shell longitudinally ovate or subglobose, more or less gibbous, acute at 
the apex. Valves subequally convex; mesial fold not strongly defined, 
one, two, or more smaller plications usually marking the centre of each 
valve : beak of the ventral valve perforate * the perforat ion generally 
well defined, the lower side formed by a deltidium which separates it 
from the umbo of the opposite valve. 
Surface radiatingly plicate or striate : shell-structure fibrous or fibro- 
punctate ? 
Valves articulating by teeth and sockets; the crura supporting two 
conical spires, which occupy the greater part of the cavity of the two 
valves. The cardinal process of the dorsal valve is a broad subemargi- 
nate plate, spreading laterally and a little recurved at its basal margins, 
where it is clasped by the teeth of the opposite valve, and extends 
beneath the deltidium, lying close against the inner surface of that part 
of the ventral valve. 
The mode of articulation, as now determined, is very similar to that of Nucleo- 
spira; but the cardinal process is proportionally shorter and emarginate at the 
extremity, the perforation of the beak large and distinct, while the form is different 
and the exterior surface plicate or striate, and not punctate as in that genus. 
The form of the species is not unlike Rhynchonella , but usually more symmetri¬ 
cally rounded, and with less distinct mesial sinuosities. In these characters they 
resemble Waldheimia, to which genus I had originally referred them until the 
discovery of the internal spires. 
Several of these shells bear a close resemblance, both in the general form and in 
the interior spires, to Retzia; but the dorsal valve never presents the straight ex¬ 
tended hinge-line, nor the ventral valve the short area, common to the carboniferous 
species of that genus. 
