CHIEFLY IN NORTHUMBEBLAND AND DURHAM. 36S 



exhibits under the microscope, when placed in a favourable light, 

 a delicately reticulated or tesselated structure (shown in figs. 

 1, 2, towards the posterior extremity) ; the surface is smooth 

 and shining, pale green, beautifully but irregularly banded with 

 dark green and orange. In my specimens the normal coloration 

 seems to consist of an encircling fillet of orange with a trans- 

 verse broad pellucid band behind the middle, and a sharply de- 

 fined black patch over the eyes, beneath which are several dark 

 green cloudy patches ; but the appearances vary so largely, 

 according to the method of illumination, that it is difficult to 

 describe correctly even a single specimen, of which no two are 

 exactly alike. Length, -rs-th of an inch. Setae of lower aw^ 

 tennas very short, as in C. rejJtans, 



I at first supposed that this might be the male of C. virens, 

 which species occurred abundantly in the same gathering, but 

 further examination showed the supposition to be incorrect, all 

 my specimens being females. Some doubt may perhaps be en- 

 tertained as to its identity with MiUler and Jurine's species, but 

 though their written descriptions are often very characteristic, 

 their figures can scarcely be depended upon for perfect accuracy, 

 and I am the more disposed to consider the reference correct, 

 from Miiller's description of the shell structure, " aucta valde 

 magnitudine testa tessellata sive reticulata apparet, baud tapieji 

 pellucida." His description of the coloration agrees also closely 

 with that of my specimens. Professor Lilljeborg's figures agree 

 well with rQ.y examples and evidently refer to the same species j 

 but Fischer has unaccountably identified Miiller's C. ornata with 

 the C. virens of Jurine [tristriata, Baird), the figui'es given by 

 the two authors being widely different, much more so indeed 

 than the species themselves actually are. Fischer's figures refe}? 

 undoubtedly to C. virens, and not to the present species, 



Genus. POTAMOCYPRIS, nov. gen, 



Carapace compressed, reniform ; shell calcareous and rather 

 thick, valves unequal, the right much the larger and overlapping 

 on the dorsal and in the middle of the ventral margin : dorsal 



