552 BRITISH PALAXOZOIC FOSSILS. [CEPHALOPopa. 
In this species, according to M. de Koninck, the inner lip and sides of the mouth become greatly thickened ; 
the keel (although still undefined) more prominent, and the obliquely arched lamellar costz larger, but more 
irregular in the adult specimens of two or three inches in diameter; I have not seen, however, any speci- 
mens in this condition. M. de Koninck supposes the B. apertus of Sowerby to be the internal cast of this 
species, but the umbilicus is manifestly of greater proportional diameter in the true B. apertus, of which I 
have examined large numbers from the original locality. In the moderately young specimens the band is quite 
flat, and almost smooth; in older specimens it is distinctly crossed by arched imbrications of growth. The acute 
angle at which the transverse ridges meet the band, and the wide, undefined keel, separate the species easily 
from the B. tangentialis, with which it is confounded in d’Orbigny’s Monograph. 
Position and Locality Rare in the carboniferous limestone of Derbyshire ; casts in the red carboniferous 
limestone of Breedon, Leicestershire. 
BELLEROPHON DECUSSATUS? (/’lem.) 
Ref. and Syn.—? Flem. Brit. Anim. p. 338. = B. elegans D’Orb. + B. clathratus @ Orb. Monog. Bellerophon, t. 7. 
f. 12 to 18. and t. 5. f. 24 to 27.=B. reticulatus M°Coy, Synop. Carb. Foss. Irel. t. 2. f. 2. 
Dese.—Globose ; umbilicus very small, deep, rounded, exposing the edge of the inner whorls; margin of 
the sides and umbilicus very tumid; mouth transversely reniform ; keel broad, obtuse ; moderately prominent, 
sharply defined; surface covered with sharp, subequal, subregular, thread-like spiral ridges (eight or nine in one 
line at two lines in diameter), separated by flat spaces, slightly exceeding their own width, reticulated by 
slightly arched transverse strize usually nearly equalling the spiral ones in size, but slightly further apart, and in 
general direction nearly at right angles to the keel, except close to the point of junction, where they are slightly 
bent backwards ; the points of intersection of the spiral and transverse threads are slightly turbercular ; keel 
with from three to five longitudinal strize like those of the sides, and similarly reticulated; semicircular cal- 
losity of the inner lip very thin; substance of the shell very thin. Diameter of small specimens about three 
lines, proportional width at mouth (no abrupt dilatation) =, antero-posterior diameter of mouth “4, diameter 
of umbilicus nearly =. 
According to de Koninck this species, when adult, reaches two inches in diameter, and loses the reti- 
culation near the sides of the umbilicus, the edges of the mouth and the inner lip becoming greatly thickened. 
I have seen no specimens exhibiting those characters. In my volume on the Mountain Limestone Fossils of 
Ireland, I describe this species under the new name B. reticulatus, on account of Phillips’s statement, that 
the axis in Fleming's species was solid; de Koninck and D’Orbigny, however, agree now in ascribing an um- 
bilicus to the true B. decussatus; and I think it better therefore to abandon my name and follow them. 
Position and Locality—Common in the black beds over the main carboniferous limestone of Derbyshire ; 
common in the carboniferous limestone of Fifeshire. Very large specimens (one and quarter inches in diameter) 
are not very uncommon in the impure carboniferous limestone of Lowick, but having the surface so imper- 
fectly preserved, that the reticulation can only be seen in spots near the edge. 
A few remarkable specimens in the collection from the black marble beds of Derbyshire are possibly 
adults of the above species, having a very thin, curved, reflected margin three lines wide round the mouth ; 
width, including margin, one inch eight lines, entire length, including mouth and reflected margin, about 3, 
length of mouth exclusive of margin ;;;, width of do. {5 diameter of umbilicus ;;; surface indistinctly preserved, 
but the spiral strie averaging eight in the space of one line, band prominent, rather more than half a line 
wide. Small specimen seven lines in diameter, with traces of broad reflected lip overarching the umbilicus, as 
in the adult. Proportional width of mouth (the reflected edge broken off) =<, length of mouth 4, diameter 
of umbilicus +. 
The B. hyalinus of de Ryckholt (Mélange Paléont. t. 8. f. 26) seems to agree very closely with the 
adult specimens, but has not the keel so strongly marked. 
