100 SYNOPSIS OF THE CHARACTERS OF THE 



This curious little species resembles the recent P. ohsoletus in having the maj-gin only marked with ra- 

 diating ribs or stria, which disappearing at about half the length of the shell from the beak, leave all the middle 

 of the shell and the region of the beaks perfectly smooth. Length eight lines, -svidth three and a half lines. 



Pecten seruatus. M'Coy. (PI. XVII. fig. 8). 



Sp. Ch. — Longitudinally ovate, depressed; ears very large, unequal; surface with about thirty narrow, 

 equal, radiating ribs, closely set with pointed scales ; posterior ear pointed, with one or two longitudinal undula- 

 tions of the shell ; anterior ear rounded, deeply divided from the body of the shell, with four or five rounded, 

 longitudinal ridges, crossed by erect, waving, scaly lines of growth. 



This elegant species is perfectly unlike any other vnt\\ which I am acquainted ; the spaces between the 

 numerous serrated ribs are smooth. Length six lines, width six lines. 



Pecten simplex. Phil. 



Pecten simplex. Pliil. Geol. York Avicula simplex. Koninck. Fos. Bel. 



Sp. Ch. — Obliquely ovate; width two-thirds the length; left valve gibbous, right valve nearly flat; pos- 

 terior side steeply truncated ; beaks prominent ; hinge-line oblique, less than the ■svidth of the shell ; ears very 

 small, equal, nearly square ; surface marked with strong, obtuse, radiating ridges ; intervening spaces transversely 

 striated. 



This pretty little species cannot with propriety be included either in Pecten or Avicula, and a new" group 

 is much wanting to include it and a number of other fossils. 



Pecten Sowerbii. M'Coy. (PI. XIV. fig. 1). 



Sp. Ch. — Elliptical, convex in the middle ; ears small, equal, acute, conate ; surface concentrically striated. 



This very beautiful species is distinguished from all the others of the carboniferous limestone by the form 

 of its ears, which are equal, acute, and conate, being considerably elevated above the beak of the shell, as we 

 see in some Oolitic species ; the surface is concentrically striated. Length one inch one line, width one inch. 



Pecten spiNULosus. M'Coy. (PL XVII. fig. 1). 



Sp. Ch. — Longitudinally ovate, convex; ears large, nearly equal; anterior rounded, posterior pointed; 

 body of the shell radiated with about twenty-six sharp, regularly spinose ridges, between each pair of which 

 intervenes one much finer rib, also regularly set with spines at the same distances as those on the larger ridges ; 

 ears with close, radiating ridges, crossed by sharp, imbricating striae. 



The spines arc placed at such regular distances on the ribs of this little species, that they seem to form 

 concentric, as well as longitudinal rows; they are cylindrical, solid, and placed rather far apart; the ears are 

 remarkably large, nearly equal, and square. Length three and a half lines, width three and a half lines. 



Pecten tabtjlatus. M'Coy. (PL XVI. fig. 12). 



Sp. CVt.— Lengthened, ovate, flat; ears nearly equal; posterior ear roimded, with two or three longitudinal 

 folds, crossed by very strong, scaly striae, parallel to the margin ; anterior ear acute, falcate, with fine striae pa- 

 rallel to the curved margin. This ear is deeply divided from the body of the shell by a steep space ; surface of 

 the shell with about fifteen fiat ribs, separated by very narrow, deep sulci ; each rib branches as it reaches the 

 margin. 



This little species is remarkable for the perfect flatness of the body of its shell, which is, nevertheless, of 

 considerable depth, being much elevated above the plane of the ears, from which it is consequently separated by 

 a very steep plane. Length about six lines, width six lines. 



