218 PNEUMONOBRANCHIATA. 



Shell about half an inch long, glossy black or 

 grey, often marked with short cinereous streaks, with 

 regular raised lines, which, when closely examined, 

 appear a little granular; spire composed of from 

 seven to ten rather raised volutions ; aperture oval, 

 with the inner lip a little contracted, with three plaits, 

 all on the pillar, the lower one interior and hardly 

 distinguishable in the full-grown shell; the margin 

 thick and white, but not reflected, detached all 

 round. 



This very common species varies greatly in size, 

 in the slenderness and ventricoseness of the shell, and 

 in the strength or slightness of the concentric striae, 

 but in a large series all these varieties gradually and 

 uninterruptedly pass into one another, and they may 

 all be found in specimens collected from the same 

 locality. It is also rarely found transparent and 

 colourless. Mr. Jeffreys describes a distorted spe- 

 cimen, with a prominent medial ridge down the 

 whorls. 



Mr. Alder has kindly communicated to me " a 

 specimen of the shell he sent to Dr. Turton, which 

 Dr. Turton calls C. parvula (t. 5. f. 59.) ; and also the 

 specimens of the true C. parvula (according to Fe- 

 russac), found in Germany, for comparison." He 

 further observes, that all the British specimens he 

 has seen, he thinks, are only varieties of C. nigricans y 

 which, I think, the specimen fully bears out. 



