CYPRINA. 305 



nexuous, occupying rather more than one-third of the circum- 

 ference : teeth, in the rigjit valve three cardinals, the middle one 

 strong and short (from which the other two diverge), the ante- 

 rior triangular, and posterior ridge- like ; lateral tooth indistinct ; 

 the left valve has likewise three cardinals, two of which 

 on the anterior side are symmetrical and very short, and the 

 third is laminar and diverges from the centre ; lateral tooth 

 strong and distinct ; the hinge is also furnished with several 

 irregular tooth-like processes on the anterior side: inside chalky- 

 white and nearly smooth: paUial scar broad and shining: 

 muscular scars large and distinct, but not remarkably deep. 

 L. 4. B. 4-25. 



Yar. crassior. Shell thicker, more round, and somewhat 

 compressed : epidermis of a darker hue and occasionally pitch- 

 black. 



Habitat: Common in sand mixed with mud, on 

 every part of the British coasts, from low-water mark to 

 100 fathoms. The variety occurs in Swansea, Cardigan, 

 and Bideford bays. This species is a member of all our 

 newer tertiaries, and peculiarly characteristic of glacial 

 deposits. Every sea of northern Europe and North 

 America still contains it in a living state, its southern 

 limit appearing to be the Boulonnais and Cherbourg. A 

 more globose variety (C. csqualis, J. Sowerby) is found 

 in pliocene strata at Nice and in Sicily. This form is 

 the C. islandicoides of Lamarck. 



Hugh Miller says, in his pleasant l Sketch-book of 

 Popular Geology/ that C. Islandica, " although one of 

 the most common shells of the boulder-clay, is by no 

 means one of the most common shells at the present 

 time of our Scottish coasts." This must be a mistake ; 

 for in the Moray Firth, the scene of the gifted geologist's 

 labours, recent shells of this species are very much more 

 abundant than the fossil remains of specimens entombed 

 in the boulder-clay or " till." But in a postglacial or 

 raised beach at Goldspie in Sutherlandshire, close to the 

 brink of high- water mark, I noticed that valves were 



