428 MR. G. S. BRADY'S MONOGRAPH OF 



6. CTTHBBIDBA sorbyaxa, Jones. (Plate XXIX. figs. 1-6.) 



('[ithende 



of Tert. Form. p. 44, pi. iv, figs. 6a-6e. 



Nor 



inermis, idem (left valve), ibidem, p. 56. 



Scandin 



^ 



ivian type (?). Distribution : Recent— Norway, Scotland. Fossil— Glacial, Scotland and Nor- 

 way; crag, England. 



( ferapace, as seen from the side, broadly subtriangular, highest in front of the middle; 



greatest height equal to two-thirds of the length. Anterior margin broadly rounded, 

 posterior obliquely rounded, narrowed, and exserted below; theright valve bears on the 

 anterior margin six blunt teeth ; and its postero-ventral angle has one much longer tooth, 

 which is directed downwards and backwards. Superior margin boldly arched, somewhat 

 "ibbous in front of the middle, sloping with a steep curve behind; inferior margin 



lightly convex in front, straight behind. Outline, as seen from above, broadly oval, 

 with equally rounded extremities, widest in the middle ; greatest width equal to two- 

 thirds of the length. Surface marked with irregular concentric rugse, which are most 

 pronounced towards the margins, and bearing numerous short and rigid scattered hairs, 

 which are papillose at the base. The left valve is much larger, higher, and more 

 rounded, and less attenuated behind than the right, besides being destitute of marginal 



teeth. Animal unknown. 

 Length -3V in. 



Hah. Off Lewis [Admiralty soundings) ; Hebrides (Mr. J. G. Jeffreys'* dredgings) ; off Ormeshead (Mr. D. 



Robertson) . 



G. O. Sars, having seen only separated valves of this species, has naturally referred 

 them to two distmet specific forms, which is not surprising, considering the great 

 dissimilarity between the right and left valves. I had myself adopted the same course 

 until I saw a perfect carapace (posttertiary fossil), collected by the Rev. H. W. Crosskey 

 mi Norway ; this at once showed me the mistake. I have figured the Norwegian shell 

 for the sake of better illustration (figs. 2-4), all hitherto found recent specimens con- 

 Mstmg merely of detached valves. 



7. Cy-thekidba zetlandica, n. sp. (Plate XXVIII. figs. 42-46.) 



Valves, as seen from the side, oblong subreniform ; greatest height near the posterior 

 extremit , equal to more than half the length. Anterior and posterior margins obliquely 

 rounded; the anterior narrow; the posterior broad and subtruncate. Dorsal margin 

 forming a flattened arch ; ventral straight, with a slight median sinuation. Seen from 

 above, the carapace is oval, widest in the middle, rather obtusely pointed in front, 

 broader behind ; greatest width equal to half the length. End view obovate, broadly 

 rounded above, pointed below. Lucid spots about five in number ; irregularly angular 

 and rather crowded together. Surface smooth, dull yellowish white. Animal unknown. 



Length 4* m. 



D V11 2 7 



The general appearance of C. zetlandica is very like that of Candona Candida; it has 

 no h„w,v, T , the polish of the freshwater species. Two or three specimens taken by 

 Mr. Barlee m rock-pools m Shetland, and now in Mr. Norman's collection, are the only 





