PECTINID^E. 41 



and truncate. Hinge-line straight and short. Umbones small, oblique, pointed, 

 placed about the junction of the anterior and middle thirds of the hinge-line. The 

 anterior ear small and depressed, not very sharply defined from the rest of the 

 valve. The posterior ear much depressed, narrow, and its posterior superior angle 

 greater than a right angle. The valve obliquely swollen and its greatesl convexity 

 nearer the posterior than the anterior border. The dorsal slope 1 well marked and 

 broad, forming a broad oblique hollow groove which lies between the ear and an 

 oblique angular ridge, which forms the posterior margin of the valve. 



Interior. Unknown. 



Exterior. — The surface is ornamented with numerous broad, flat, radiating 

 libs, some of which bifurcate as they pass across the shell. The ribs are broader, 

 and the grooves that separate them less deep, in the anterior part of the valve. 

 The ribs are crossed by concentric ruga? and lines of growth. The ears are 

 without radiating- ridges and have only lines of growth. 



Dimensions. — PL XIX, fig. 17, a left valve from Settle, measures — 

 Antero-posteriorly . . . . 4G mm. 



Dorso-ventrally . . . .24 mm. 



Gibbosity of valve . . . 7"5 mm. 



Localities— -The Carboniferous Limestone of Settle, Yorkshire, and Park Hill, 

 Derbyshire. 



Observations. — This species differs from J', simplex in its great obliquity, and 

 possesses more numerous and flatter ribs than that species. A series of three 

 specimens from Settle, one of which (PL XIX, fig. 18) is bivalved, are in the Wood- 

 wardian Museum, Cambridge, and I have three specimens in my cabinet from 

 Park Hill, Derbyshire. Unfortunately the hinge-line is not quite perfect in any of 

 them, and the anterior ear is not well exposed. The peculiar characters of the 

 species are so well marked that it is not likely to be confounded with any other. 

 The radiating ribs are not well marked in young examples or in the ambonal 

 region of the full-grown specimens. 



Family PECTINIDJE. 



The Pectiniform shells of the Carboniferous period have been referred to 

 various genera by different authors. Phillips described his specimens as Avicula 

 and Pecten. Portlock used the term Pecten, but referred one tine example to 

 Orthis. M'Coy subdivided his species among the genera Pecten, Aidcula, Limn. 

 Malleus, Meleagrina, Pterinea, and Monotis ; but later on he proposed the new 

 genus Aoiculojpecten, to which he referred the majority of Carboniferous Pectini- 

 form shells. The type of this new genus was .1. planoradiatus, which subsequently 



