OS 



Mean divergence about 10^; lengtli .27 incli ; greatest brcadlli 

 .004 inch ; least breadth .OaG inch. 



CvLrxDHELLA COSTULOSA. Siiell fusi form, Well elongatcd : Avhi- 

 tisli : with prominent .=^orae\v]iat oblique ribs, of which there are about 

 fourteen or tifteen on each whorl, and which are niore crowded and 

 le.ss prominent on the last whorl ; with distinct crowded stride parallel 



with the ribs: .spire truncate with the loss of whorls; whorls 



remaining seven or eight, flattened, with a deep suture : last whorl 

 much detached and produced, obtusely angulated on the right and 

 anterior sides ; aperture dilated, angulated anteriorly and on the right ; 

 lip well expanded, moderately reflected, shai-p. For the loan of this 

 species I am indebted to INIr. Cuming. 



Length .04 inch ; bread.th .00 inch. 



[ I'o BK CoMI.NUI.D ] 



On page 33 we described ILUx sulphurea as ' perhaps a young 

 slicll.' This opinion was founded on its papyraceous appearance. 

 Mr. Chitty, from v.'hom the original specimens v.'ere received, has re- 

 cently furnished a series, which shews that this shell, with all the generic 

 characters of Helix, is the last embryonic stage of the West Indian 

 variety oi' DoHum perdix / In a mature D, perdix, this nucleus may 

 be distinguished. In a young shell, near the apex, may be very easily 

 ■seen a clearly defined margin of the nucleus, at which margin the 

 smooth and polished nuclear surface is abruptly succeeded by the close 

 spiral stri-<B which characterise the West Indian D. perdix. In the 

 ■change from a continuous to a notched aperture, the anterior extrem- 

 ity becomes first angular, and before the next whorl is completed, the 

 notch is perfect. 



This example is instructive, not only as illustrating our depend- 

 (ence for true generic types on the soft parts, but also as indicatingthe 

 inferior rank of the Ilelicidae as compared with the Purpuridae. A 

 distinguished Zoologist has recently suggested that air-breathing ani- 

 mals are of higher rank than aquatic families of the same class. But 

 80 far as may be inferred from the embryonic history of the shells, 

 the Lamarckian system is sustained in its gcncn'al outlines. 



Iha synonymy of Hdix picturata (v. p. 30) needs some elucida- 

 tion, and we offer the following remarks in the hope of contributing 

 to this object. By some authors this shell has been mistaken for IT. 

 siimata Mull. Dr. Pfeiffer, with his usual discrimination, accurate- 



