159 
Chonetes? variolaris, 
Chonetes papilionacea, 
55 
55 
papilionaceus, 
papilionacea. 
55 
55 
De Keyserling, 1846, Reise in das Petschoraland, p. 215, pi. 6, 
fig. 2. 
L. Gr. de Koninck, 1847, Eech. Anim. Poss., I, p. 187, pi. 19. 
fig. 2. 
P. V. Semenow, 1854, Ueber Poss. Bracb. Scbles. Kohlenkalkes, 
p. 30, pi. 1, fig. 2. 
McCoy, 1855, Brit. Pal. Poss., p. 455. 
B, d’Bicliwald, 1860, Lethjea Eossica, I, p. 876. 
M. y. Grriinewaldt, 1860, Mem. Acad. Imp. Petersbourg, II (7), 
p. 110. 
T. Davidson, 1861, Mon. Brit. Carb. Brack., p. 182, pi. 46, fig. 3-6. 
This shell is transverse, sub-circular, depressed, very slightly vaulted, 
and, indeed, occasionally almost quite flat ; its hinge line is straight, occupying 
the greatest width of the shell. The ventral valve is slightly convex, especially 
in the median portion ; its beak is scarcely perceptible, and not prominent ; 
its hinge area is well developed, and provided with a deltoidal fissure partly 
covered by a pseudodeltidium. The dorsal valve is slightly concave, and 
follows, at a short distance, the curves of the ventral valve ; its hinge area is 
narrower than that of the ventraT valve, and its rather well-developed cardinal 
process partly closes the deltoidal fissure of that valve. The exterior surface 
of both valves is covered with innumerable fine radiating ribs, the thickness 
of which scarcely varies throughout their whole length ; they multiply by 
simple bifurcation. When the shell, which is very thin, is partly removed, 
what remains of the ribs is granulated, and seems to bristle with numerous 
rather pointed tubercles, beside which are small punctures like pin-pricks, 
due to the perforation of the shell. The hinge line of the ventral valve is 
furnished with a series of small tuherculate spines, about one millimetre apart. 
The internal structure of the valves is only known to me in part, but the 
dotted strim, observable in most specimens of Chonetes, are strongly marked. 
Dimensions. — This species can acquire very great dimensions, and reach 
a breadth of from twelve to fifteen centimetres. An almost perfect specimen, 
sent me by Mr. W. B. Clarke, measures thirty-three millimetres broad by 
seventeen long. 
Delations and Differences. — This species, in its size, approaches C. 
como'ides, Sowerby, but differs from it by being nearly flat, and by the slight 
* [The text has “ dorsal ” here, but “ ventral ” is obviously intended. — T.W.E.D.] 
