210 BRITISH PALAXOZOIC FOSSILS. [Bracuropopa. 
shew the usual hood-shaped piece within the beak of the great valve, from the ridge of which a thick but short 
mesial plate extends to the surface (forming a short slit in the cast); in the small valve are two short lamelle 
diverging at an angle of 33°, and between them, but not reaching the beak, is a very delicate mesial septum (as 
in the P. oblongus); small valve shews two impressions on each side of the beak nearly parallel with the 
hinge-line, but connected with the diverging plates by an inward curve, the muscular impressions are within 
the diverging plates. Length of small specimen (of small valye) eleven lines, width about the same, depth 
about three and half lines. 
This species has exactly the same internal structure as the P. oblongus, but having all the internal plates 
much shorter, the cast of the receiving valve sometimes shews the mesial septum, and sometimes the two 
diverging plates ; the latter I suspect scarcely reach the inner surface of the large valve, and the former probably 
scarcely projected from it, so that a slight difference of level in the cast brings one or the other into view; it is 
externally distinguished from that species by the widest part being nearer the beak, and the more prominent 
rounded, prolonged mesial ridge in front. 
Position and Locality —Rare in the olive Upper Bala shale of Coniston, Lancashire ; common in the Bala 
sandstone of Mandinam, Caermarthenshire. 
PENTAMERUS MICROCAMERUS (J/°Coy). 
Syn. and Ref. = Spirifer ? levis Sow. Sil. Syst. t. 21. f. 12. (not Pentamerus levis Sow.) = Pent. 
microcamerus M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VIII. p. 390. 
Sp. Ch.—Transversely elliptical, receiving valve depressed, gently convex, greatest depth near the beak, 
which is elevated nearly at right angles, the height being one-eighth the width of the hinge; entering 
valve gently convex; beak small, rather prominent, reaching to the plane of the lateral 
margins, with which the low, triangular area is nearly parallel; greatest depth slightly 
behind the middle; a broad, faintly marked, slightly convex, obsolete mesial ridge, and 
a few faint, broad, obsolete, irregular, lateral radiations ; hinge-line slightly less than 
the width of the shell; side margins elliptically rounded, front margins very wide, 
ee gently convex ; cardinal area nearly sixteen times wider than high ; surface apparently 
smooth, or with a very minute fibrous longitudinal striation ; internal cast of receiv- 
ing valve shewing the broad triangular boss of the foramen slightly keeled ; the mesial 
Upper Figure,—Internal cast Septum formed by the junction of the bounding lateral lamellze of the foramen only 
See ap netcaritealise aad reaching one-third the length of the shell, or a little more than equal to the width 
small rostral chamber, formed : . : . 
by the converging of the dental Of the rostral chamber; cast of entering valve with a very narrow triangular area in 
shoe Figure Rostra part of the plane of the lateral margins, two very slightly diverging dental lamellz, scarcely 
dinal_ ares, andivery small di- reaching twice the width of the area, (or one-eighth the length of the shell), exterior 
edges of which form two more diverging slits resembling cardinal teeth; a slight 
indication of a mesial septum, commencing a little in front of the ends of the diverging lamellee, from between 
the ends of which project two long spatulate muscular impressions, not reaching quite to the middle of 
the shell. Width two inches six lines, proportional length =, depth of receiving valve ;;,, of entering valve 
about the same. 
I have recently examined so great a number of specimens of this species from May Hill, that there can 
be no longer any doubt that it belongs, not to the genus Spirifer, as suggested by Mr Sowerby, nor to the 
genus Orthis, as suggested by the Palzeontologists of the Geological Survey, but is a distinctly defined species 
of Pentamerus, distinguished by the very small size of the rostral chamber in the receiving valve, and the 
extreme shortness of the diverging lamellie in the entering valve, which are not even indicated in Mr Sowerby’s 
figure thereof. As the species must be placed in the genus Pentamerus, and there is already a Pentamerus 
levis, 1 am obliged to propose a new specific name. In yery young specimens three lines long the mesial 
septum exceeds half the length of the shell. 
Position and Locality.—In the fine sandstone of Mandinam, Caermarthenshire. Very abundant in the 
sandstone of May Hill, Gloucestershire. 
SS 
