1 24 CARBONIFEROUS LAMBLLIBRANCHIATA. 



posterior margins flattened. The hinge-line short and straight. The inferior 

 margin broad and convex, meeting the slightly convex anterior and posterior 

 margins at a rounded, obtuse angle. The ears very small and not raised; the 

 umbones small, pointed, central, that of the left valve the more convex. 



Interior. — The internal surface is crossed by well-marked, broad, radiating 

 grooves and ribs. Pallia! line remote from the margin. 



Exterior. — The surface is marked by broad radiating ribs and sulci, the ribs 

 being about twice the breadth of the grooves. The ribs often appear subdivided. 

 They are absent for a small space near the posterior border, and are almost 

 obsolete in front. The ribs and sulci are crossed by very close, fine, concentric 

 lines of growth. 



Dimensions. — PL XXI, fig. 3, a left valve, measures — 



Antero-posteriorly . . . .57 mm. 



Dorso-ventrally . . . .45 mm. 



Depth of left valve about . . .6 mm. 



Locality. — Ireland : Carboniferous Limestone, Cork and Little Island, co. Cork. 



Observations. — This species was founded on specimens from Little Island, co. 

 Cork, two large examples being in the collection of Mr. Joseph Wright, of Belfast 

 (PI. XXI, figs. 1 and 3). Fig. 1 represents a right valve with a portion of the test 

 preserved, showing the general contour of the valve and its anterior ear. Fig. 3 

 represents a cast of the left valve, a little incomplete at the hinge-line. In this 

 species the broad radiating ribs are present on the surface, and by this character 

 the species is easily identified. 



M'Coy's type-specimen is preserved in the Griffith Collection of the Museum 

 of Science and Art, Dublin. It is a left valve (PI. XXI, fig. 2), not quite 

 complete, and was very badly represented by the inaccurate figure in M'Coy's 

 work. The hinge-line and general obliquity of the shell are inventions of the 

 artist, and unfortunately the description seems to have been drawn up from the 

 figure rather than from the specimen. M'Coy doubted whether he was correct in 

 referring this shell to Pecten, I think on good grounds, though I do not consider 

 thai the shell has any close relation to Lima. He says, " I have much doubt 

 whether this shell really belongs to the genus Pecten ; it is at least an aberrant type, 

 and if placed in this genus it leads to Lima, and if placed in Lima it leads back to 

 the present genus." 



