320 Mr. E. A. Smith on African MoUusca. 



I cannot discover any good reasons for separating Lea's 

 SpatJia natalensis from this species, and it is remarkable that, 

 in his account of it, he did not refer to Waldhergi. The form, 

 sculpture, epidermis, and muscular scars are precisely the 

 same ; but the interior of Wahlhergi is described as whitish 

 for the most part, but pale flesh-colour towards the middle. 

 On the other hand, the nacre of natalensis is described as 

 purple. This difference of colour, however, is not of any 

 material importance, for it is well known to be a very variable 

 character in Unionida?. 



II. Demoulia. 



This genus was founded by Gray for the reception of 

 Buccinum retusum of Lamarck and a new species from 

 Senegal, namely D. pulclira. The latter, the type of which, 

 from Gray's collection, is now in the British Museum, is iden- 

 tical with D. pinguis described by A. Adams some thirteen 

 years later. 



D. reiusa and another species, D. abhreviata, have spiral 

 sculpture only, and in this respect they are peculiar. But 

 this is not sutlicient to found a genus upon. If we admit 

 differences of sculpture to be of generic importance, we could 

 make half a dozen or more genera out of Nassa itself. 



On the other hand, D. pulclira^ which, in form and general 

 aspect, agrees with the two species mentioned, differs from 

 them in having the spiral strife crossed by longitudinal lines, 

 thus producing a fine reticulation. It will thus be seen that 

 the character of spiral sulci and ridges is inconstant. 



In the genus Nassa the form and surface-ornamentation is 

 notably variable, and examples may be selected, e, g. X glans 

 and N. tliersites, which are f;ir more dissimilar in both 

 respects than the species of Denwuh'a are from many forms 

 of Nassa. Nassa Ciimingii, for instance, has quite the shape 

 of DemouUa, and really differs only in having the transverse 

 ridges beaded instead of smooth. Moreover, D. ringens has 

 very similar granular sculpture ; and if we separate D. allre- 

 viata and I), reiusa on account of their having smooth trans- 

 verse sculpture, then we must remove ringens to another 

 group. 



Gray * considered that the " velvety periostracum " 

 afforded a character which would separate it from Nassa. 

 Difference of epidermis, however, is not a generic character, 

 for how many species of Comis, Pectunculus, and other genera 



* Aim. Nat. Hist. 18o(>. vol. i. j). i"J. 



I 



