41 
which have really no median furrow. Therefore the subject 
requires considerable study, and the division between certain 
forms of Aulacothyris and Zeilleria will have to be clearly defined. 
TEREBRATULA PisoLiTHica, S. Buck. Plate ITI, fig. la, b, ¢. 
Shell nearly circular, biplicated, the furrows not extending 
one-third up the valves; furrows rather shallow, somewhat 
close together, and projected forward beyond the regular curve 
of the dorsal valve; middle furrow in dorsal valve shallower 
than the laterals, slightly larger than the furrows in the 
ventral valve; valves moderately and almost equally convex; 
beak fairly well developed, incurved, slightly overhanging the 
dorsal valve, separated from it by a rather small space, and 
almost concealing the deltidial plates; foramen* circular, but 
with an outer area, of which the outer rim has its lower 
portion flattened, and its two lower corners projecting more 
or less. 
This is a biplicated species, which has for a long time been 
observed in the Cotteswolds, though it has not been figured or 
described, so far as Iam aware, but has generally been con- 
sidered a variety of first one species and then another. The 
species to which it is nearest allied are Terebratula ifra-ooli- 
thica, Desu., which occurs in the opalium zone in Dorset and 
Somerset, Terebratula. ewides, S. Bucx., Murchisone zone, 
Dorset,t and Terebratula Stephani, Dav., Parkinsoni zone, 
Dorset and Somerset. T. infra-oolithica however has the length 
of its two valves nearly equal, the beak obliquely truncated, 
not incurved, and with longer beak ridges.t Terebratula ewides 
differs by its laterally pinched beak, prominent beak ridges,§ 
and conspicuous carina down the larger valve. Terebratula 
Stephani, (in its typical form,) is best distinguished from our 
* This kind of foramen is possessed by Terebratula simplex, BucK., and 
is well shown in Davinson’s Brachiopoda, Plate VIII, figs. 1 and 2. 
+ L lately described this species in the “ Geological Magazine,” May, 1886, 
page 218. See Dav. Brach. Ap. to Sup. pl. 19, fig. 4, T. Flerscheri (non 
Oppel). 
{ Vide. fig. 3. 
§ Vide. fig. 2. 
