Distribution of the British Ostracoda. 61 



tion, covered in up to the edge of the valve Avith a thin trans- 

 parent coating of shell. When closely examined, the Norwe- 

 gian specimens likewise exhibit traces of this structm-e, but 

 very indistinctly. 



Argilloecia cylindrica, G. O. Sars. 



A few specimens which appeared to be referable to this 

 species were dredged off Greenock Pier. Further examina- 

 tion of the living animal, however, is needful before we can 

 pronounce positively as to its identity. 



Pontocypris hispida^ G. O. Sars. 



Some very fine and well -characterized examples were 

 dredged off Cumbrae; and we have some even finer from 

 Ventry Bay, Ireland. From a careful comparison of these 

 with undoubted specimens of P. mytiloides^ we think there 

 can be no doubt that the two forms are only varieties of one 

 and the same species. The chief distinctive characters, ac- 

 cording to Sars, are as follows : — 



P. mytiloidesj dark brown, sparingly hispid, with short 



hairs ; 8 posterior serrations. 

 P. hispida, yellowish, densely hispid, with long hairs ; 



5 posterior serrations. 



Some of our examples of P. hispida, however, are even 

 darker in colour than is usual with P. mytiloides ; the degree 

 of pubescence is subject to very great variation ; and the same 

 may be said of the number and prominence of the marginal 

 serratures : of the anatomical differences pointed out by Sars, 

 all we can say is that we have failed to detect any such in our 

 specimens. Under these circumstances, we cannot hesitate 

 to class both forms under the specific name mytiloides. 



Cytheropteron inornatum, n. sp. PI. II. figs. 1-3. 



Carapace, as seen from the side, subrhomboidal, highest in 

 the middle, greatest height equal to about two thirds of the 

 length : anterior extremity narrowed, obliquely rounded ; 

 posterior produced in the middle into a very broad, subtrun- 

 cate beak : superior margin well arched ; inferior almost 

 straight, slightly sinuated in front of the middle, and curved 

 upwards behind. Seen from above, broadly triangular, the 

 base or posterior side of the triangle produced into a very 

 large central mucro ; lateral angles almost rectangular, the 

 sides thence tapering evenly with a very slight curve to the 

 acuminate anterior extremity ; greatest width equal to nearly 



