254 CYCLADJ2. 



116. 3. CYCLAS pallida. Shell oblong, pale whitish 

 Fig. ei. yellow on the circumference, 

 slightly concentrically striated, 

 rounded before, rounded and ra- 

 ther truncated behind; sides 

 C. pallida. rather swollen, evenly convex; 

 the cardinal edge rather produced, nearly 

 straight, and slightly compressed on each side 

 the umbo ; the umbo regularly convex, rather 

 in front of the middle of the shell, sometimes 

 slightly crumpled. The foot very large; the 

 siphons elongate, united nearly to the tip ; the 

 apices conical, the upper the smallest. The 

 young are compressed, rather rounded, gra- 

 dually becoming more gibbous and elongated as 

 they increase in size. 



Sphserium pallidum. Gray, Ann. and Mag. N. H. vii. 465. 

 1856. 



Inhab. Grand Junction Canal near Kensal Green. 



The largest specimens are -- of an inch long, 

 ^-J- high, and -^ thick. The average-sized specimens 

 are \ inch long, -J- thick, and ^V high. 



The living specimens emitted, when in confinement, 

 several young shells about 1 line long. 



They are decidedly distinct from any of our British 

 specimens, but bear a very great resemblance to 

 Cyclas rhomboidea of Say, found in the rivers of 

 North America. "We have unfortunately only a 

 single specimen of this species in the British Museum, 

 which was sent from the Ohio by Mr. Anthony. 

 This example only differs from the specimens found 

 by Mr. Rowse in the front side being rather at- 



