CYCLAS. 119 



binet," that we have drawn up our description of a shell 

 which we have never observed as British elsewhere, and 

 which, even as avowedly foreign, is of very rare occurrence 

 in the cabinets of Great Britain. 



Shell subrhornbic, elongated, ovate, thin, inequilateral, 

 rather compressed, especially below, where the valves meet 

 each other at an acute angle, yet a little swollen immedi- 

 ately beneath the umbones. Surface with rugose concentric 

 striulse, covered with a rather dull epidermis of a cinereous 

 or yellowish ash -colour, with some indistinct grey linear rays 

 towards the margin. Hinge-margin rectilinear, but higher 

 behind than in front, scarcely at all declining on either 

 side. Ventral edge arcuated near the middle, ascending 

 rather considerably in front, thus attenuating the anterior 

 side below. Posterior side decidedly, though not so very 

 greatly, the longer, subbiangulate, the lower corner being, 

 however, more or less rounded off; posterior edge not 

 much rounded. Anterior extremity much the narrower, 

 obliquely rounded below, obtusely subangulated above. 

 Umbones semitransparent, very little projecting, broad and 

 blunt. Dorsal area edged with opaque white. 



The largest individual measured five lines in length, and 

 seven in breadth. The general look of the species was that 

 of a greatly produced caliculata, devoid of the characteristic 

 prominent beaks. We did not venture to open the valves, 

 but the interior is described by Pfeiffer as having a pale 

 bluish tinge, and Draparnaud tells us that the central teeth 

 are not apparent, and the lateral very small. Brown's 

 figure does not at all agree with the shell w r e have been de- 

 scribing, nor his assertion that its general contour is more 

 orbicular than others of the genus. We have not ventured 

 to cite either the Tellina lacustris of Muller, or the Cyclas 

 lacustris of Nilsson, as the umbo of the former is stated to 

 be acute, the contour of the latter to be orbicular-sub- 

 rhombic. 



