602 THE UPPER SILURIAN. 



Clidophorus subovatus, Hall. Shell, broadly oval or ovate, moder- 

 ately and evenly convex ; beaks near the anterior end ; umbones 

 moderately elevated ; a scarcely defined depression extending from 

 the umbo towards the postero-basal extremity; anterior extremity 

 rounded, posterior extremity unknown (? regularly rounded) ; clavicle 

 extending half way from the anterior cardinal margin to the base 

 of the shell. Surface marked by fine unequal sub-lamellose 

 stria?. 



This shell is larger and more regularly convex than any of the 

 others here described, and more inequilateral than any except the 

 G. cuneatus. Arisaig, coll. J. W. D. 



Nuculiies (Orthonota) carinata, Hall (Fig. 207). Shell extremely 

 elongate, nearly three times as long as wide ; sides sub-parallel ; 

 hinge-line straight, beaks appressed, sub-anterior, the anterior ex- 

 tremity rounded; posterior extremity obliquely truncate, longer 

 on the hinge-line than on the basal margin. Surface marked by a 

 sharp carina which extends from the umbo obliquely to the postero- 

 basal angle ; the space anterior to this carina marked by distinct 

 elevated lamellose striae, and intermediate • finer ones. The space 

 between this and the cardinal line smooth and slightly depressed. 

 Cardinal line anterior to the beak showing six or seven crenulations. 

 A strong clavicle extends from the anterior cardinal line with a 

 gentle curve nearly to the base of the shell. Arisaig, coll. J. W. D. 



Fig. 207. Fig. 208. Fig. 209. 



Nucidites carinata. Tellinomya attcmuxta. Heganibonia cancdlata. 



This shell presents characters not before observed combined in 

 one species. It has the general form of Orthonta, while the crenu- 

 lated cardinal line and the anterior clavicle are characters of Nuculites. 

 The shell is readily distinguished from species of either genus hereto- 

 fore described. The Orthonotse, yet known, have the surface marking 

 much less sharply defined. 



Tellinomya attenuata, Hall (Fig. 208). Shell elongate, narrow, 

 more than twice as long as high, anterior end short and rounded ; 

 beak elevated, situated a little in advance of anterior third, posterior 

 end narrow and abruptly rounded ; basal margin slightly curved, 

 and impressed posterior to the centre ; posterior cardinal line straight 

 but gradually declining; contour evenly convex. Surface concen- 

 trically striated, shell thick. 





