CerHaLopopa. ] UPPER PALZOZOIC MOLLUSCA. 555 
(very rarely with a slight backward inclination at the extremity), uniting obliquely into bundles at the edge of 
the umbilicus, to which they form tangents; averaging four or five transverse ridges in three lines near the 
keel at one inch in diameter; mouth transversely reniform, rounded at the sides. Width of mouth of small 
specimen one inch one line, proportional diameter ;5, antero-posterior diameter of mouth *, diameter of umbilicus 
=, width of keel rather less than half a line. 
MM. @Orbigny and de Koninck believe the B. cornu-arietis (Sow.) to be the internal cast of this species, 
but I have ascertained that this is not so (see description of B. cornu-arietis, p. 551). 
Position and Locality —Not uncommon in the carboniferous limestone of Derbyshire. 
BELLEROPHON TENUIFASCIA (So7.) 
Ref.—Sow. Min. Con. t. 470. f. 2, 3. 
Desc.—Globose ; periphery and sides very convex ; umbilicus small; mouth transversely reniform, slightly 
reflected at the sides. Surface often almost smooth, with fine, obsolete, very slightly arched strize, having a small 
backward curve at the point of junction with the keel, which they meet at an angle of 75°; keel simple, promi- 
nent, very delicate, thread-like (imperceptible in parts of many specimens) ; shell thin. Diameter of rather 
small specimen ten lines, width of mouth the same, proportional length of mouth 4, width of umbilicus 7, width 
of keel one fourth of a line. Cast very gibbous, sides slightly flattened, sloping, with a small, rounded, pro- 
minent-edged umbilicus. 
I have not myself seen perfect casts of this species, but Sowerby’s figure of the cast indicates a pro- 
16 
portional diameter of the umbilicus of only ,;, at most. 
Position and Locality —Rare in the carboniferous limestone of Derbyshire. 
BELLEROPHON UREI (Flem.) 
Ref. and Syn.—Flem. Brit. Anim. p. 338; Phill. Geol. York. Vol. II. t. 17. f. 11, 12; Portk. Geol. Rep. 
t. 29. f. 9. =B. atlantoides VOrb. Mon. Bel. t. 4. f. 14 to 19. 
Dese.—Globular; periphery very broadly rounded ; umbilicus only marked by a small shallow depression ; 
mouth wide, transversely reniform, not abruptly expanded. Surface (at five lines in diameter) covered by about 
twenty-eight strong, nearly equal, spiral ridges (about six in two lines at the above diameter), separated by rather 
narrower, deep sulci, the two middle ridges marking the band slightly smaller than the adjoining ones. Cast 
having the periphery slightly flattened, the umbilicus large, and the surface almost smooth, or with faint traces 
of spiral sulci. Average diameter five or six lines, width of mouth slightly more, length of mouth about “%, 
proportional width of umbilicus in casts about =. 
According to de Koninck, the adult specimens become smooth near the mouth. 
Position and Locality——Not uncommon in the coal-shale near Glasgow; a variety with more distinct 
umbilicus and wider sulci between the ridges, in the black beds over the main limestone of Derbyshire. 
Genus. PORCELLIA. (L’£veillé). 
Gen. Char.—Discoid, depressed; whorls very slightly embracing, exposed in a very wide umbilicus, 
slightly deeper on one side than the other, from a trifling obliquity of the first one or two turns; a narrow 
band extends along the middle of the exterior, ending in a narrow slit in the lip; surface often nodular, 
and ornamented with rough strix. 
The depressed discoid form, and a very slight obliquity of the enrolment of the young whorls, distinguish 
this genus from Bellerophon. 
