FOSSILS. 601 



cardinal line curving, with a scarcely defined ridge along the uni- 

 bonial slope ; basal margin strongly rounded, sinuate on the postero- 

 basal margin and regularly rounded, with a scarcely defined ridge 

 extending down the slope just anterior to the clavicle. Surface finely 

 striated concentrically, a slightly curving clavicle extending from the 

 cardinal line nearly two-thirds the distance to the anterior basal margin. 



This species differs from the preceding in the equal length and 

 breadth, and consequent greater proportional height, in the sinuosity 

 of the postero-basal margin, and more abruptly-rounded basal outline, 

 and the curving forward of the beaks. Arisaig. 



CUdophorus eluuffcdus, Hall (Fig. 206). Shell sub-elliptical, 

 length about twice the height, beaks much nearer to the anterior 

 end, which is narrowly rounded ; umbones rounded, prominent ; a 

 defined gradually widening depi'ession extends from the p- « ^ 

 umbo to the posterior basal margin, causing a straighten- c. eiongatu^. 

 ing or slight sinuosity in the edge of the shell ; a defined 

 ridge along the posterior slope between the sinus and the 

 cardinal margin. Surface very finely striated. A slender 

 clavicle extends from the anterior cardinal margin a little more than 

 half-way to the base, and curving slightly forward. 



This species differs externally from all the others in the greater 

 proportional length and in the rounded umbones. 



The C. cuneatus of the same size is a stronger and proportionally 

 higher shell, having a less defined sinus on the posterior slope, and 

 a much stronger clavicle. Arisaig, coll. J. AV. D. 



CUdophorus semi-radiatus, Hall. Shell somewhat oval-ovate, length 

 about one-third greater than the height. 



Surface marked by fine concentric band -like stria?, and the posterior 

 slope by flattened dichotomized radiating stria?, the two sets of strias 

 gradually dying out at their junction. A faint line anterior to the 

 beak marks the place of the clavicle. Arisaig, coll. J. W. D. 



CUdophorus nucidiformis^ Hall. Shell nearly equilateral, sub- 

 ventricose, height and length as seven to nine. Anterior end rounded, 

 basal margin regularly curved; posterior end sub-acute, a slight 

 flattening or depression along the posterior umbonial slope, and be- 

 tween this and the cardinal line a narrow ridge. On the anterior 

 slope there is a depressed line almost jiarallel to the cardinal line, 

 marking apparently the course of the clavicle. Surface marked by 

 fine concentric stria?. 



This species resembles in form the C. concentricus in its equilateral 

 form, but the fine unequal concentric stria? and the difference in direc- 

 tion of the clavicle arc sufficient to distinguish it. Arisaig, coll. J. W. D. 



