from the River Scheldt and the Grecian Archipelago. 49 



Cytherura flavescens, nov. sp. (PL VIII. figs. 13-15.) 



Carapace, seen from the side, oblong, constricted in the middle; 

 height fully equal to half the length ; anterior extremity 

 rounded, posterior produced in the middle into a short ob- 

 tuse beak : superior and inferior margins both distinctly 

 sinuated in the middle. Outline, as seen from above, ovate, 

 mucronate behind, pointed in front ; greatest width situate 

 in the middle, much less than the height. Surface of the 

 valves marked with delicate raised reticulations, the longi- 

 tudinal markings being most conspicuous. Colour yellowish. 

 Length -^ inch. 



I have specimens of this species also from the estuary of the 

 Thames, and perhaps from other British localities ; but the 

 genus to which it belongs is so perplexing, the species being 

 numerous and separated by such apparently variable charac- 

 ters, that I had not hitherto ventured to describe it under a 

 distinct specific name. These foreign specimens, however, 

 appear to place the species on a more certain foundation. 



Cytheropteron acutum, nov. sp. (PL VIII. figs. 1-4.) 



Carapace, seen from the side, oblong, subrhomboidal ; greatest 

 height in the middle, equal to half the length : anterior ex- 

 tremity rounded ; posterior obliquely truncate, produced 

 above the middle into an obtuse beak : superior margin 

 arched, inferior sinuated in front of the middle. Seen from 

 above, the outline is diamond-shaped, widest behind the 

 middle ; extremities acuminate, width greater than height. 

 Surface of the shell smooth, marked with small, distant, 

 circular papillae ; lateral ala prominent. Length -^ inch. 



Cytherideis teres, nov. sp. (PL VIII. figs. 5, 6.) 



Carapace, as seen from the side, elongated, oat-shaped, higher 

 behind than in front; greatest height in the middle, and. 

 equal to one-third of the length ; anterior extremity rather 

 attenuated, posterior rounded : superior margin evenly 

 arched, inferior almost straight. Seen from above, com- 

 pressed ovate, acutely pointed in front, more obtusely be- 

 hind, widest in the middle ; width equal to the height. 

 Surface of the shell smooth. Colour yellowish white. 

 Length Vf inch. 



Polycope, sp. (Plate VII. figs. 15, 16.) 



A few separated valves of a species of Polycope, not much 

 different in appearance from P. orbicularis, Sars, but smooth 



Ann. & Mag. N. Hist. Ser. 4. Vol iii. 4 



