356 CARBONIFEROUS LAMELLIBRANCHIATA. 



Exterior. — The surface is ornamented with many regular very fine lines of 

 growth, parallel to the contour of the shell. Shell thin. 



Dimensions. — PI. XXXIX, fig. 35, a specimen from Poolvash, Isle of Man, in 

 the collection of Mr. R. Law, measures — 



Antero-posteriorly . . . .16 mm. 



Dorso-ventrally . . . .12 mm. 



From side to side . . . .8 mm. 



Localities. — England: the Carboniferous Limestone of Settle, Yorkshire; in 

 shale above the Underset Limestone, Faraday Gill, West Flank of the Nine 

 Standards, near Kirkby Stephen, and the Shelly Limestone of Poolvash, Isle of 

 Man. 



Observations. — This species was described by de Ryckholt under the term 

 Trapezium an?ise, and was referred to Sanguinolites byde Koninck (op. supra cit.). 

 It has, however, a far greater affinity to G. Sehjsiana, the hinge of which has been 

 isolated, and on these grounds I have removed it to the genus Cypricardella. The 

 shape of the shell is peculiar, being almost a true lozenge. The oblique ridge is 

 more pronounced and more nearly vertical than in G. Sehjsiana, apparently dividing 

 the valve into two equal triangular portions. The postero-superior angle is so 

 much produced backwards beyond the rest of the valve that the posterior margin 

 is obliquely truncate downwards and forwards, and the postero-inferior angle is 

 beneath the umbo. 



I am inclined to think that the Nucula carinata of M'Coy may have belonged 

 to this species. The type of this shell is still preserved in the Griffith Collection 

 of the Science and Art Museum, Dublin, but it is so imperfect and badly preserved 

 that I am unable to be absolutely certain as to what it really is. 1 have therefore 

 felt unable to adopt this name, which is prior to that of de Ryckholt. 



Cypricardella rectangttlaris, M'Coy, sp. Plate XXXIX, figs. 20—26. 



? Nucula. rectangulaius, M'Coy, 1844. Synops. Carb. Toss. Ireland, p. 71, pi. xi, 



fig. 20. 



Specific Characters. — Shell very inequilateral, transversely rectangular, com- 

 pressed, keeled. The anterior end is very short, and narrowed from above 

 downwards, being only about half the height of the other dorso-ventral diameters 

 of the valve. Its border is rounded, the antero-superior and inferior angles 

 being obsolete. The inferior border is nearly straight, almost parallel to the 

 binge-line. The posterior border is truncate and nearly straight, almost vertical, 

 willi well-marked postero-superior and inferior angles. The hinge-line is arched 

 in front, straight, somewhat raised, and produced posteriorly, as long as the 



