THE MAKQUIS DE EOLIN ON THE C^CIDiE. 259 



tlie operculum is in reality the only distinctive cliaracter of 

 Brochina, it is important to inquire whether such a character is 

 sufficient, and whether it is peculiar to a class of shells sus- 

 ceptible of constituting a genus. At present the number of 

 species appears to be reduced to a single one. This is very 

 little ; and I have remarked in various specimens belonging to 

 this species such an affinity with shells diverging widely from 

 the diagnosis of the genus, that I have been led to entertain 

 doubts on the subject. 



In January 1867, I published, in the ' Journal de Conchy- 

 liologie,' two new species of Brocliina, B. Someri and B. achi- 

 rona, differing from each other only in the form and size of the 

 septum. The specimens came from Brazil, and appeared in all 

 respects to accord with the generic diagnosis — aperture acute 

 and operculum convex in the centre, flat at the margin, and very 

 thick, so as actually to appear convex. I accordingly placed 

 the shells under the genus Brochina. Some time afterwards 

 we received other samples of the sea-bottom from the same 

 anchorage, and in the sand were found other specimens of the 

 same species, amongst which some appeared to be marked 

 with a longitudinal ornamentation ; and I soon discovered that 

 some of them were distinguished by a set of strong and wide 

 longitudinal strice, which in others appeared gradually to di- 

 minish in distinctness, until at last they entirely disappeared in 

 the smooth shells. This showed at once that there was no longer 

 any question of these shells not belonging to the genus Brochina, 

 and that the shells first referred to were smooth forms of (JcBcum, 

 of which there existed a variety — striata. This circumstance 

 having awakened my suspicions respecting the genus, I en- 

 deavoured to collect a great number of specimens of Brochina 

 glabra, and to examine the specific characters in many indivi- 

 duals. I sent for specimens from England and examined 

 them carefully. They did not seem to correspond exactly with 

 Dr. Gray's diagnosis. "When the shell was full-grown and com- 

 plete, I remarked that the aperture was not acute, but, on the 

 contrary, surrounded by a narrow reflected border, of whose 

 existence we were assured by observing an almost insensible en- 

 largement (enjlure) near the base by the narrowing of which the 

 aperture was contracted, at the end of which contraction was a 

 very minute groove, beyond which rose the reflected border above 

 referred to. 



