BRACHIOPODA. 
123 
siderable amount of calcareous matter in it; no signs of punctation to be seen 
with a half-inch objective. Valves, convex, the lower valve varying in amount 
of convexity with its habitat, but always more or less inflated. A small, sharp, 
longitudinal septum rises from the center of the lower valve, of a subtriangular 
shape, covering and hiding a small tubular perforation of the apex of the shell. 
This perforation is very oblique, and from its internal opening a groove extends 
backward nearly half-way to the posterior border of the shell inside. The an¬ 
terior muscular scars meet in front of the septum .and form a semilunar eleva¬ 
tion with the points directed backward. The posterior scars in the lower valve 
are small and widely separated. On the external surface the foramen appears 
nearly in the middle of the shell and the furrow is continued anteriorly for a 
short distance. (There is no furrow in my specimens outside behind the fora¬ 
men, which is the only point of difference from Sowerby’s figure.) Upper 
valve convex, apex subcentral; a slight median longitudinal callus internally. 
There is no strongly impressed disc about the foramen as in Discinisca, though 
slight traces of a differentiated area exist there.”* 
Discina striata, Schumacher, is the only known representative of this genus. 
(See Plate IV k, figs. 23, 24.) Its minute, almost imperceptible foramen (so 
small that both Schumacher and Gould, not seeing it, referred the species to 
Crania), and the arrangement of its internal impressions, separate it by a full 
generic difference from its nearest allies. With Discina, therefore, we have at 
present nothing to do among the palaeozoic brachiopods. 
The foregoing limitation of the genus Discina by Mr. Dall left all the other 
recent species, currently referred to that group, without a designation, and for 
these the author proposed the term Discinisca, with the following definition :f 
“ Sub-genus Discinisca, Dall, = Discina, Auct. Lower valve more or less 
flattened, concave or compressed, Upper valve more convex; apices of both 
subcentral or subposterior. Lower valve with a small septum as in Discina, 
behind which is an impressed disc or area, externally concave and internally 
elevated. This is perforated by a longitudinal fissure, extending from a short 
distance behind the septum nearly to the posterior margin, which is often 
slightly indented behind it. Shell more or less horny in texture, minutely 
tubulose. Type, Discina lamellosa, Broderip.”| 
* Bull. Mus. Comp. Zool., vol. viii, No. 1, p. 39. 
t Bull. Mus. Comp. Zool., vol. iii, No. 1, p. 37. 
| Proc. Zool. Soc., 1833, p. 124. 
