90 DEVONIAN FAUNA. 
convex. Inferior margin moderately convex. Postero-inferior corner very 
convex and slightly produced. Contour of back regularly and flatly convex, 
spreading out to the lower margins. Valves meeting at a very acute angle. 
Surface bearing about thirty equal rounded ribs, separated by similar furrows, 
and slightly smaller in the anterior part of the shell, which have the appearance, 
which is probably deceptive, of being crossed by transverse strie. 
Size.-—Length 18 mm., width 18 mm., depth of both valves about 7 mm. 
Locality.—A single specimen from Wolborough is in the Museum of Practical 
Geology. 
Remarks.—The specimen here described is that which Phillips figured as 
Pecten plicatus, Sowerby.’ It is such a worn and indistinct fossil that it is 
very difficult to decide its true character. It might almost be supposed to be a 
Ehynchonella were it not for the inequilateral character of the ribs, and its close 
resemblance to some species of Aviculopecten. The appearance of wings is very 
doubtful, and, if remaining at all, they are certainly much injured and confused 
with matrix. Phillips gives an enlarged portion showing transverse marks, but 
those in the specimen are really so indistinct that it is more than doubtful whether 
they are not simply due to fossilisation in a granular matrix. 
It appears to differ from Pecten plicatus, Sowerby, as given by Phillips,’ from 
Yorkshire, by the greater width of the anterior side and by having much fewer 
ribs. From Pecten newilis, Sowerby,’ it differs still more in the same particulars. 
From P. plicatus, Sow., as originally described, it differs in the same particulars, 
and in having the base of the shell much more regularly semicircular, so that I do 
not think it can possibly be the same species. 
On the other hand, it very closely resembles P. Oceani, both as originally 
described by Goldfuss, and as given by Frech. Both figures are rather longer 
and more oblique, but they both have the appearance of being drawn from shells 
that might not have preserved their true shape, and they differ as much from each 
other as they do from the present shell. There would be little doubt of its identity 
if the two points of the smoothness of the ribs and the existence of wings could 
be asserted. The former has been already discussed, and Frech speaks of some 
transverse markings in the German shell. As to the latter point all that can be 
said is that two projections very like wings exist, but their state of preservation 
makes it impossible to be certain that they really belong to the fossil. On the 
whole, the probability is that the English shell belongs to the German species. 
Affinities.—From Crenipecten comma it certainly differs by its ribs being larger, 
closer, and not alternating. 
1 1827, Sowerby, ‘ Min. Conch.,’ vol. vi, p. 144, pl. dlxxiv, fig. 3. 
2 1836, Phillips, ‘ Geol. Yorks.,’ vol. ii, p. 212, pl. vi, fig. 21. 
3 1840, Sowerby, ‘Geol. Trans.,’ ser. 2, vol. v, pt. 3, p. 58, figs. 1, 2. 
