Mr. E. A. Smith on African Mollusca. 321 



tlicre are wliich arc clothed with periostraca of entirely difFc- 

 rciit kinds. 



Tlic animal of Demoulia has hitherto been unknown 

 excepting the operculum, described by H. and A. Adams'*. 

 However, through the liberality of Mr. J. H. Ponsonby, who 

 has lately presented to the British Museum a specimen of D. 

 retusa containing the animal, I am able to give the following 

 particulars. 



The sole of the foot (in alcohol) is uniform light brown. 

 The head and body are also light brown, irregularly speckled 

 with black. The foot is short, squarish in front, with a 

 double edge, rounded behind, and cq^j^arently without prolon- 

 gations as in Nassa ; but it is possible that, being contracted 

 in spirit, they are not visible, or may have got broken off. 

 The head is compressed j the tentacles are short, acuminate, 

 with the eyes on prominences about halfway up the outer 

 side. The siphonal fold of the mantle is darkish at the end 

 and moderately short. The radula f is Nassoid ; the lateral 

 tooth on each side is oblique, bicuspid, the outer cusp being 

 largest, with the acute tip curved inwards and the inner cusp 

 more slender and also slightly incurved. The central tooth 

 is arcuate, as broad or broader than the laterals, and armed 

 with nine slender, acute, subequal denticles. 



The figure illustrating the dentition of Nassa variahih's 

 in Troschel's Gebiss d. Schneck. vol. ii. pi. viii. fig. 19, 

 affords a very good idea of that of the present species. 

 The laterals, however, of the Nassa have the inner cusp 

 shorter and less slender and the denticles on the central tooth 

 are more unequal in length. 



The most remarkable character about D. retusa is the 

 want of an operculum. 



From the above remarks it will be seen that there really 

 exist no good characters to separate Demoulia from Nassa. 

 There is nothing in the formation of the shell which distin- 

 guishes it, and the structure of the animal is exactly the same 

 in both, and the fact that the operculum in one species 

 [pulchra) is present, and wanting in another {'retusa), shows 

 that it is not an essential generic character. 



This genus was originally described by Gray under the 

 name Demoulia, and there is no valid reason why the spelling 

 of this word should be changed. Gray himself appears to 

 have been the first to make an alteration, and in the ' Pro- 

 ceedings of the Zoological Society ' for 1847, p. 140, he 



* Gen. Moll. vol. i. p. 115, pi. xii. fig. 6 a. 



t I have to thank my fi-iend Mr. B. B. Woodward for kindly mounting 

 this with his ctccustouied skill. 



