Bracuiopopa.] UPPER PALAZOZOIC MOLLUSCA. 411 
with a few fine concentric strize and interruptions of growth under the lens, closely reticulated with fine 
punctures, smaller than those of S. hastata. Length of very large adult specimen one inch six lines, propor- 
tional length of entering valve =, width =, depth of entering valve =, depth of receiving valve 2, breadth of 
front =, proportional width of specimen ten lines long %,, depth of both valves 4, (probably a little crushed); 
proportional width of specimen eight lines long 4, depth of both valves ~. 
It will be seen from the above proportional measurements, that according as the specimens decrease in size 
they gradually assume exactly the proportional width of Sowerby’s figure, and as they increase in size the 
proportional length increases ; the figures of Phillips are wider than Sowerby’s figure, or any specimen I haye 
seen. . This species is distinguished from the others by the broad portion of the ovate outline being towards 
the beak instead of towards the front, owing to the great width of the rostral portion and the rather small 
depressed beak; the unusually long, anterior, lateral margins are nearly straight, and converge gradually to the 
narrow front ; they being longer than the posterior lateral margins gives a curious peculiarity to the outline of 
the species; and as well as the perfect absence of mesial hollow on the receiving valve, and the strongly 
marked, elongate, flattened space or angulation at the posterior lateral margins, and general depression, distin- 
guish it from its allies. 
Position and Locality.—Not very uncommon in the carboniferous limestone of Derbyshire; the very small, 
but otherwise identical specimen figured by Mr Sowerby is quoted from the Devonian limestone of Plymouth. 
SEMINULA sAccuLus (Mart. Sp.) 
Ref. and Syn. = Anomites sacculus Martin, Pet. Derb. t. 46. f. 1, 2 = Terebratula id. Sow. Min. Con. t. 446. 
f. 1. left-hand figure ; Phill. Geol. York. Vol. II. t. 12. f. 2. 
Desc.—Longitudinally ovato-pentagonal, small, very gibbous, margins very obtuse ; greatest width at about 
one-third the length from the front margin; front rather abruptly narrowed, with a deep rounded notch, from 
which a moderately wide, concave, mesial sulcus, equally deep in both valves, extends to within about four lines 
of the beak of the entering valve, about the same length from the front margin, but not so near the beak in the 
receiving valve; front margin not raised, but perfectly in the plane of the lateral margins; receiving valve 
obscurely pentagonal or subtrigonal; beak very large, prominent, much incurved, with an obscure angulation 
on the sides; foramen rather narrow, oval; profile regularly arched; greatest depth about the middle of the 
length; middle portion gibbous, gently convex except towards the front, where it is indented by the mesial 
hollow; sides tumid, rapidly falling to the very obtuse margins; entering valve rotundato-pentagonal, very 
gibbous ; profile slightly and regularly arched ; sides tumid, sloping very rapidly from the mesial third, which is 
flattened towards the beak, impressed by the mesial furrow towards the margin; surface with occasional con- 
centric, rather coarse lines of growth, minutely reticulo-punctate under the lens. Length of very old, large 
specimen, with much thickened margins, eleven lines; proportional length of entering valve 4, width 4, depth 
of receiving valve ;;, depth of entering valve =, width of front #4; length of average-sized younger specimen 
seven lines, width +, depth of both valves *, width of front &. 
This species is easily distinguished from the S. hastata by its small adult size, which is proved by the great 
thickening of the margins, at or under one inch in length, the deeper notch in the front, and it and the mesial 
sulcus existing at a much smaller distance from the beak than in that species; and above all, the species are 
distinguished by the great difference of angle at which the valves meet at the margin, the front and lateral 
margins of S. hastata being sharp and wedge-like, but those of S. sacculus being extremely blunt and obtuse. 
Several writers mention their inability to distinguish this species from some of the varieties of S. elongata or 
S. sufflata of the Permian rocks; but specimens perfectly identical in form and size may be readily distinguished 
by a small but distinctly marked upward wave in the front margin towards the entering valve in the Permian 
fossil, while the margin of the carboniferous species is nearly or quite horizontal. In the S. sufffata also the 
mesial septum is much longer and more strongly marked in the receiving valve, extending to within one-third of 
the length of the front margin. The punctured instead of fibrous surface, under a good lens of three-fourths of 
an inch focus, distinguishes specimens from the Hemithyris didyma. 
