CYPRICARDELLA CONCENTRICA. 351 



Interior. — The anterior adductor muscle-scar is small, round, and marginal. 



The posterior, very small, is placed immediately below the hinge-line, remote from 



the posterior end. The pallial line is entire. The hinge consists of a single 



cardinal tooth with a cavity on each side of it, and an elongate posterior lateral 



lamellar tooth in the right valve. In the left are two cardinal teeth, separated by 



a deep triangular cavity and an elongate posterior lateral tooth. Formula 



R. 0,010,1 r „, . , . ,,, . . ,. 



: — ibe interior or the valve is smooth. 



L. 0,101 ,1 



Exterior. — The surface is ornamented with regular, concentric, raised angular 

 ridges, separated by grooves which are finely striated concentrically ; these ridges 

 all terminate at the oblique ridge, only an occasional one being carried across 

 the dorsal slope, which is smooth or very finely striate. Shell moderately thick 

 for its size. 



Dimensions. — Fig. 8, PI. XXXIX, a specimen in the cabinet of Mr. J. Neilson, 

 measures — 



Antero-posteriorly . . . .17 mm. 



Dorso-ventrally . . . .14 mm. 



From side to side . . . .8 mm. 



Localities. — Scotland : the Upper Limestone series of Linn Spout, Dairy, and 

 Gare ; the Lower Limestone series of Law, near Dairy, and Craigen Glen. 



Observations. — I am of opinion that the species just described has been referred 

 to Venus elliptica of Phillips by Scotch geologists, but that shell is probably a 

 truncated and incompletely preserved specimen of Allorisma sulcata. The 

 majority of specimens which I have examined are small, but Messrs. Neilson and 

 Smith have lent me specimens, Figs. 8 and 10, PI. XXXIX, which show the 

 shell in its adult state. Mr. Smith, in addition, has examples of the shell 

 showing the hinge, fig. 10 a, PI. XXXIX. 



The majority of the species of this genus are not so strongly ribbed con- 

 centrically, but one other species, C. parallela, which occurs in the Carboniferous 

 Limestone of Hill Stebden, S.W. Yorkshire, possesses this character; here the 

 ribs are much more numerous and closer, and the shell is more gibbose, and 

 has the postero-superior angle much less elevated. The Astartella vera of Hall 

 has a very close resemblance indeed to C. concentrica, but is more gibbose, 

 transverse, and has a well-marked oblique ridge, and the concentric ridges are 

 more numerous and closer. I have been able to compare the two species 

 directly, as a series of Astartella vera were sent to me by the Smithsonian 

 Institution. 



