﻿80 DEVONIAN FAUNA. 



respects their resemblance is so close that I think it may be safely referred to 

 that genus. 



III. Sub-order. — MONOMYARIA, Lamarck, 1809. 



I. Family. — Pectinid^i, Fleming, 1828. 

 1. Genus or Sub-genus. — Pterinopecten, Hall, 1883. 



This is a section of the Aviculopectens, with a long hinge-line and large 

 undefined and subequal wings. I have retained the name as marking a prevalent 

 group, for which it is a good designation. As pointed out below, however, it 

 would have been better (if it were not for the confusion it would cause) to have 

 limited the name Aviculopecten to the present group, and to have found a new 

 designation for the shells to which Hall has restricted that name. 



These shells occur in the Devonian and Carboniferous Rocks. 



1. Pterinopecten gracilinus, Whidborne, sp. PI. IX, fig. 10; and PI. X, figs. 2, 



2 a, 3, 3 a. 



1889. Aviculopecten gbacilinus, Whidborne. Geol. Mag., dec. 3, vol. vi, 



p. 79. 



Description. — Left valve of moderate size, flat, sub-circular, slightly inequi- 

 lateral. Umbo minute, low, proximate, not elevated above the hinge-line, slightly 

 anterior, undefined. Hinge-line almost or quite as long as the shell, straight. 

 Anterior wing small, flat, narrow, acutely triangular, with a sigmoid anterior 

 margin ; and defined by a concave line running from the front of the umbo. Hind 

 wing confluent with the rest of the shell. Anterior margin very broad, with a 

 small deep notch at the base of the wing, and then obliquely convex, forming a 

 continuous curve with the inferior and posterior margins, till, in the upper part, 

 the posterior margin becomes slightly concave. Contour of surface slightly convex 

 in the central part, and sloping flatly to the margins on every side, except the 

 supero-anterior, where a sudden depression divides it from the wing. Surface 

 covered by about sixty prominent, rounded, radiating ribs, only about fifteen of 

 which arc sirn on the umbo itself, and the others start at different points, some- 

 times near the umbo, and sometimes only close to the margin ; the whole crossed 

 by much more numerous, very fine, flat, close, microscopic threads, and occasional 



