350 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 26, 



selected as the type is connected by numerous specimens with variety 

 quadrata, a short, broad, subquadrate shell. The latter is closely re- 

 lated by its outline to Cyrena Jamesoni and 0. Cunninghami, Forbes, 

 but is always slightly pointed behind, and not truncated as in the 

 allied species. 



Not having had an opportunity of critically examining the types 

 of Forbes's species from the Staffin estuarine beds, I cannot speak 

 decisively as to the subgeneric position which should be assigned to 

 the shells named by him Cyrena Jamesoni, t. v. f. 7 a, lb (?nonf. 8 a, 

 8 b), and Cyrena Cunninghami, t. v. f. 9 a, 9 b ; but I venture to pre- 

 dict that they will be found, on careful study, to be congeneric with 

 the species here described. 



Cyeena cucoxlata, nov. spec. PI. XII. fig. 10. 



Shell thick, trigonal/ tumid; umbones prominent, subcentral; 

 lunule distinct ; posteally obliquely subtruncated, rounded anteally ; 

 surface with many and close lines of growth. 



Dimensions. Length 1-2 inch, breadth 1 inch. 



Horizon. Infra-Oxfordian estuarine beds, Loch Bay, Dunvegan 

 (J-. B.). 



POTAMOMYA EOBTTSTA, nOV. Spec. PI. XII. fig. 11. 



Shell transversely ovate-oblong, subequilateral, rather tumid; 

 anterior margin rounded, posteriorly produced and arched ; umbones 

 prominent, curved; surface coarsely wrinkled concentrically with 

 the margin. 



Dimensions. Length 1-9 inch, breadth 1-2 inch, thickness -75 inch. 



Horizon. Infra-Oxfordian estuarine beds, Loch Bay, Dunvegan 

 {J.B.). 



P. robusta is related to P. ? Soiuerbyi, Forbes, in its inflated, trans- 

 versely ovate form, but differs in its more robust habit, produced 

 posterior area, and in its relative narrowness. 



Coebula hebeidica, nov. spec. PI. XII. fig. 2. 



Shell nearly equivalve, subequilateral, rotund, trapezoidal, gib- 

 bous, obliquely carinated ; posterior area very narrow and trian- 

 gular ; front margin slightly curved ; surface marked with concentric 

 folds, alternately strong and weak. 



Dimensions. Length -^ inch, breadth -^ inch, thickness -^ inch. 



Horizon. Infra-Oxfordian estuarine beds, Loch Bay, Dunvegan 

 (/. B.). 



This species has the general form of C. alata, J. Sow., but is 

 rather more elliptical, has stronger folds, the posterior area is 

 relatively narrower, and the front margin decidedly arched. 



Diteypa ciEcrxATTJM, nov. spec. 



Tube about the dimensions of Dentalium giganteum, Phil., with 

 which it has been confounded ; but the anterior one third forms a 

 semicircle, and the whole presents nodular enlargements at distant, 

 variable intervals ; aperture circular, with a bevelled margin. 



