CrepHALopopa. | UPPER PALASOZOIC MOLLUSCA. 551 
5th Class. CEPHALOPODA. See page 306. 
Ist Ord. Trrraprancuiata. See page 307. 
Ist Family. BELLEROPHONTID. See page 307. 
Genus. BELLEROPHON,. See page 308. 
BELLEROPHON CORNU-ARIETIS (Soz.) 
Ref—Sow. Min. Con. t. 469. f. 2. 
Dese.— Casts, composed of two whorls ; rapidly enlarging, and abruptly expanding at the mouth; mouth 
bilobed, and with a deep, narrow, : ngular sinus in the edge, elevated to form an obtusely angular ridge, which is 
continued, but more obscurely marked, to the apex, near which, from being bounded by two obscure sulci, it gives 
a faintly trilobate contour to the exterior; the whorls widely separated from each other ; umbilicus very large, 
obtusely excavated within. Diameter three inches, proportional diameter of last whorl =, diameter of um- 
bilicus 35, space between last and penultimate whorl about ;;,, width of mouth = at the edge, diminishing 
abruptly to = at one inch from the edge, length of mouth about % at edge, diminishing abruptly to “4 at half an 
inch within the edge. zterior: shell extremely thick; mouth dilated, retroflexed at the inner corners when 
young, and overhanging a slight semielliptical depression, not forming a true umbilicus, which with age becomes 
entirely filled by a great, smooth, rounded callosity, extending over the sides of the mouth ; beyond this callosity 
the surface is marked with coarse, obtuse, irregularly unequal, arched ridges, meeting at a moderately acute angle 
(60°), the undefined, obtusely prominent keel, over which they arch; callosity on the inner lip very large, 
rhombic, obtusely keeled in the middle of the outer margin, Diameter two and half inches, proportional width 
of mouth and lateral callosities 80°. 
MM. @Orbigny and de Koninck, in their several works, suppose the B. cornu-arietis and B. tangentialis 
to be the internal casts and the exterior of one species. I have clearly ascertained, however, that this is not 
the case, by carefully removing the external shell from one side of one of the Cambridge specimens, so as to be 
absolutely certain of the cast being Sowerby’s species, and shewing that its external shell has not hitherto been 
recognized. It has no resemblance to B. tangentialis, but is very like de Koninck’s figure of the adult B. costatus 
(Anim. Foss. Belg. t. 26. f. 2a, 6, c) in form, costation, obtusely rounded undefined keel, and callosities ; but 
the arched ridges do not meet the keel at so acute an angle in the present species, and there is no trace of 
umbilicus, or umbilical depression, in specimens of much less size than he figures; while it agrees with that, and 
differs from B. tangentialis, in the arching of the ribs, broad, rounded, undefined keel, with shallow depression 
on each side, &c.; differing from them, and all other species, in the great thickness of the shell, size of umbi- 
licus, and great separation of the whorls in the casts. 
Position and Locality—Common in the carboniferous limestone of Kendal, Westmoreland. 
BELLEROPHON COSTATUS (So7.) 
Ref.—Sow. Min. Con. t. 470. f. 4.= B. Blainvillei VOrb. Monog. Bel. t. 3. f. 1. to 3. 
Dese.— External shell; globose, moderately expanded: very slightly compressed on the sides, obtusely 
rounded on the prominent periphery; keel broad, very obtuse, undefined ; umbilicus small, deep, open; surface 
covered with subregular, imbricating, obliquely arched, lamellar ridges (averaging four in two lines, near the 
band at an inch in diameter), shewing under the lens a very fine, irregular, subparallel lineation; ridges meeting 
the keel on each side, at an angle of about 40°. Casts; smooth, globose, without marked ridges or furrows; 
umbilicus narrow, deep, with rounded sides, partially exposing the volutions. Diameter of casts, one inch, 
proportional diameter of umbilicus of the same =. 
[easc. 111. ] 4B 
