Bracuiopvopa. | UPPER PALZZOZOIC MOLLUSCA. 445 
smooth slightly convex space, from two to three lines long round the beak, beyond which three, strong, 
sharply angular ridges extend to the front margin along the top of the sinus, separated by very deep, acute, 
re-entering angles; smooth spaces forming the defined sides of the mesial ridge, very highly sloped, and 
about a third wider than the top of the sinus; sides moderately convex, depressed, with about three large 
angular ridges, slightly smaller than those of the middle, arching gradually from the margin towards the smooth 
space near the beak ; after six lines long these lateral ridges obscurely dichotomise ; profile nearly straight from 
the beak to the front margin, with a very slight downward curve at each end. Receiving valve, beak very small, 
closely incurved or adpressed to the beak of the entering valve ; triangular foramen small, rostral space for about 
two lines round the beak smooth and nearly flat, without mesial sinus; beyond this the very narrow sides are 
produced nearly in a straight line, and are gradually divided by the three great ridges; after about the same 
length the middle is abruptly curved downwards to fill the very wide strongly defined sinus in the margin; sides 
of the sinus steep, smooth ; middle with two great angular ridges. Surface under the lens marked with fine, 
irregular, imbricating strize of growth, and coarse, flexuous, longitudinal fibres of the shell-tissue. Width of 
typical specimen eight lines, proportional length of receiving valve {4, of entering valve {, width of mesial sinus 
37 
at base ,{, height thereof =, width of smooth steep side of mesial ridge in entering valve 4, depth from re- 
ceiving valve to top of sinus =. 
This species is very remarkable for its few ribs, deep trilobation (accounting for the wide, steep, smooth 
space on each side of the mesial ridge), and the very small beak. The smooth rostral space, free from ridges, 
extending nearly to the beak, clearly separates this species from any of the varieties .of H. plewrodon, and their 
great size and small number are distinctive characters from the C. ventilabrum. Some very large specimens 
from Derbyshire, nearly ten lines long, shew an obscure duplication of some of the great ridges near the margin. 
The very small depressed sides, wide space free of ridges defining the mesial elevation, and the extremely 
sharp angular definition of the ridges, separate the species from the obtuse H. pugnus. The mesial septum in 
the receiving valve, in specimens of the above size, is from three to four lines long, the divarication forming the 
chamber in the beak is very distinct, but remarkably narrow, being upwards of a line long, but considerably less 
than half a line wide. 
Position and Locality—Carboniferous limestone, Derbyshire ; carboniferous limestone of Lowick, North- 
umberland. 
Explanation of Figures.—P1. 3 D. fig. 20, extremely large specimen from the carboniferous limestone of 
Derbyshire, shewing the narrow straight sides, and extremely wide, defined, mesial hollow of the receiving 
valve; natural size, shewing one short unusual additional ridge in the sinus, and one or two at the side margins, 
from the extreme age; fig. 20a, ditto portion of fibrous shell-tissue, magnified; fig. 20 4, entering valve of 
same specimen, shewing the smooth space near the beaks, form of ridges, and the slight, unusual appearance 
of a branch or supplementary rib at the margin; fig. 20 c, profile of same specimen; fig. 21, slightly typical 
specimen, shewing the great height of the sinus, &c.; from the limestone of Lowick. 
CAMEROPHORIA SCHLOTHEIMI (V. Buch Sp.) 
Ref. and Syn. < Terebratulites lacunosus (pars) Schlot.= 7. Schlotheimi V. Buch, Ueber Terebrateln, t. 2. f. 32 = 
Camerophoria Schlotheimi + OC. multiplicata King, Perm. Foss. t. 7. f. 10 to 21, and f. 26 to 32. 
Desc.—Transversely rhombic ; lateral margins nearly in one plane ; front margin abruptly raised into a very 
wide, deep oblong sinus, slightly narrowed above ; commissure acute all round. Entering valve gibbous along the 
middle; beak small, prominent; profile regularly arched, its greatest depth in the middle of its length ; smooth, 
evenly convex, without ridges or mesial fold for about two lines from the beak, after which the sides arch much 
more abruptly to the margins than the middle, leaving a square, broad, mesial ridge, increasing in prominence 
and sharp definition with age, its sides very steep and smooth; mesial ridge with from two to eight subangular, 
subequal, longitudinal ridges; each side with from three to eight similar ridges, sometimes appearing at two 
lines from the beak, and often not till after six lines. Receiving valve moderately and evenly convex for about 
three lines from the beak, which is prominent and slightly incurved, beyond which the middle becomes de- 
pressed into a very wide, flattened, hollow, rounded by steep smooth sides to fill the sinus in the front margin, 
