410 
BULLETIN OF THE NATURAL HISTORY SOCIETY. 
The characters of this shell are obscured by flattening in the shale 
The umbo appears to be excentric, and it resembles B. CElerti, Ber- 
geron, of the Lower Ordovician of the Montaigne Noir in Southern 
France,* but has fewer whorls. Similarly to that species, the ridges on 
the shell are more distant from each other on the upper part of the 
main whorl than towards the aperture. I could not detect any flat- 
tened ridge along the keel of the dorsum. 
This shell is distinct from B. arfonensis Salter by the sharp angu- 
lation at the dorsal line, and the stride that cross it are angulated, not 
arched. 
Bellerophon semisculptus, n. sp. PI. XVIII, figs. 5. 
Only the last whorl known. This is free from the inner part of 
the coil. The proximal part is smooth with faint concentric undula- 
tions of growth. 
The lines of growth arch backward toward both ventral and dorsal 
side, and at the dorsum there is an elevated flattened keel, separated 
from the lateral slopes by a slight furrow ; the striae that run back- 
wards to this keel traverse it at right angles. 
Sculpture . — The outer two-thirds of the whorl is marked by sharp- 
edged, concentric ridges of growth ; at first there are about four in the 
space of a millimetre, then they become more distant with flattened 
spaces between, and toward the orifice of the shell there are about two 
ridges in the same space. Between the ridges, and on the smooth 
part of the whorl, the surface of the shell is minutely granulated. 
Size . — Only one example is known, which is 7 mm. across from the 
back of the whorl to the mouth, and 6 mm. across from the ventral 
side of the mouth to the dorsal keel. 
This species resembles B. hippopus, Salter, of the Arenig horizon 
in Wales. It differs in its smaller size and in the very regular ridges 
of growth ; there being no alternation of weak and strong ridges. 
From B. arfonensis^ of the same author, it differs in the raised keel in 
place of a depressed band along the dorsum. 
♦Etude geologique du Massif Ancien situe au sud du Plateau Central, J. Bergeron, 
Paris, 1889, p. .343, pi. iv, figs. 10 and 11. 
