Silurian Fossils of Nova Scotia. 



149 



fined sinus which, expanding, extends to the postcro-basal extre- 

 mity, while a less defined ridge bounds this sinuosity on its 

 anterior side ; surface marked by fine irregular concentric striae. 

 In the casts of this shell there is a strong linear straight clavi- 

 cle, extending from a point just anterior to the beak two-thirds 

 across the valve. 



Fig. 6. Fig. 1. Fig. 8. 



14. Clidophorus concentricus. N. sp. Fig. 7. 



Shell sub-equilateral, very broadly oval-ovate, the anterior end 

 the broader ; height nearly four-fifths the greatest length ; anterior 

 side a little shorter and more broadly rounded at the extremity ; 

 a slight depressed sinus on the posterior umbonial slope, which is 

 more anterior than in the preceding species. Surface marked by 

 even band-like concentric striae ; shell thin ; a linear curving cla- 

 vicle extends from the cardinal line just anterior to the beak 

 more than half way to the base. 



The prominent points of distinction between this and the pre- 

 ceding shell are the nearly central beaks, the band-like striae, and 

 the curving clavicle with the broad and nearly equal extremities 

 of the valve. 



15. Clidophorus erectus. N". sp. Fig. 8. 



Shell somewhat rhomboid-ovate, the height and length about 

 equal ; umbones prominent, beaks nearer the anterior end, some- 

 what curved and elevated ; posterior cardinal line curving, with a 

 scarcely defined ridge along the umbonial slope ; basal margin 

 strongly rounded, sinuate on the postero-basal margin and regu- 

 larly rounded, with a scarcely defined ridge extending down the 

 slope just anterior to the clavicle. Surface finely striated concen- 

 trically, 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 sinu- 

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

 basal outline, and the curving forward of the beaks. 



