342 CARBONIFEROUS LAMELLIBRANCHIATA. 



and backwards from the umbo to the postero-inferior angle is a strong well- 

 marked angular ridge, which divides the shell into two almost equal triangular 

 portions, which are inclined to each other at an obtuse angle. The inferior and 

 lower is compressed and hollowed from before backwards just in front of the 

 ridge, but becomes convex in the anterior part of the valve. The upper and 

 posterior triangle is gently convex, and forms the dorsal slope, but becomes com- 

 pressed and expanded towards the posterior border. Lunule well developed. 

 Escutcheon large and broad. 



Interior. — The anterior adductor muscle-scar is large, deep, and rough, and 

 occupies almost the whole of the cavity of the anterior portion of the shell, and is 

 surrounded behind by a broad ridge of moderate dimensions. The posterior 

 adductor scar is large, smooth, deep posteriorly, and placed immediately below 

 the superior border some distance from the posterior end. The anterior part of 

 the hinge has not been exposed, but posteriorly there is evidence of a simple 

 edentulous, rolled, hinge edge. The pallial line is well marked, entire, and 

 remote from the margin. 



Exterior. — The surface is covered with fine, almost obsolete, close, concentric 

 lines and strias of growth, which in the front part of the valve become near the 

 lower edge collected into bundles separated by deeper grooves. Towards the 

 posterior edge the lines of growth are stronger, and may become almost imbricate. 

 Shell thin. 



Dimensions. — The type specimen of Phillips's Cypricardia rhombea, PI. 

 XXXVIII, fig. 8, measures— 



Antero-posteriorly . . . .30 mm. 



Dorso-ventrally . . . .'18 mm. 



Greatest lateral gibbosity of single valve . . 7 mm. 



A very large specimen from the Isle of Man, in the collection of Mr. Law, 

 PI. XXXVIII, fig. 11, measures— 



Antero-posteriorly .... "90 mm. 



Dorso-ventrally . . . . *38 mm. 



Laterally . . . . .14 mm. 



Localities. — England : the Carboniferous Limestone of Hill Bolton and Settle, 

 and the Bolland District of Yorkshire ; Wetton, North Staffordshire ; Thorpe 

 Cloud, Dovedale, and Castleton, Derbyshire ; the Upper Shelly Limestone of 

 Poolvash, Isle of Man. Ireland: the Carboniferous Limestone of Ballycahane, 

 co. Limerick. 



Observations. — Under the names Cypricardia rhombea and G. glabrata, Phillips 

 described two shells from the Carboniferous Limestone of Bolland, of which the 

 type of the former only is still preserved. This is in the Gilbertson Collection of 

 the Museum of Natural History, South Kensington, and I am kindly permitted 



