272 Mr. W. Clark on the Genus Assiminia. 



XXV. — Observations on the Genus Assiminia. 

 ' fHs By William Clark, Esq. 



-Off rf:)id>' 

 ^8i :iR<'i^ To the Editors of the Annals of Natural History, 



- Gentlemen, Norfolk Crescent, Bath, Sept. 11, 1855. 



In your September Number, 1855, p. 183, Dr. Gray has con- 

 troverted my opinion, that the so-called genus Assiminia, em- 

 bracing the single species A. Gray ana, belongs to the Trunca- 

 tella of Risso. 



He says, " Mr. Clark's description proves the converse of his 

 position ;'' and observes, " that Truncatella should have a subcy- 

 lindrical shell with a slender tapering tip, which falls oiF when 

 the shell approaches adult age ; hence the name of the genus : 

 Assiminia has a broad conic shell with an acute tip which does 

 not fall off; if it is to be a species of the same genus, the name 

 of the latter ought to be changed. 



" The foot of Truncatella is small and peculiarly formed, and 

 the eyes of all the species, according to Mr. Clark's observations, 

 are large, with a white iris ; now this is not the case with Assi- 

 minia, and yet Mr. Clark regards it as a Truncatella" 



It appears by the first part of Dr. Gray's remarks, that he has 

 adopted the old conchological generic base for Truncatella from 

 a particular species : that definition has long been disused, and 

 did not even conchologically satisfy the requirements of science 

 when M. Philippi wrote; — as proof, that eminent naturalist, in the 

 2nd part, p. 133, of his ' Enumeratio MoUuscorum Sicilise,' thus 

 remarks on the animal of Truncatella : — 



" Tale animal testas tantopere diversas habitat, at vix ac ne 

 vix quidem characteres illis communes invenire possumus, sub- 

 cylindricas nempe, apice dcmum decollatas, globoso-conoideas, 

 imo discoideas. Illi quibus banc ob causam nomen Truncatella; 

 non placet, nomine Choristoma a De Cristophoris et Jan pro- 

 posito utantur, ne novo nomine scientiam jam nominibus gra- 

 vatam onerent." 



And Philippi illustrates these views by four figures, tab. 24. 

 f. 2, 3, 4, 5 ; three of them differ from Dr. Gray's definition by 

 their contours and by their apices never becoming decollated : 

 the 4th greatly resembles the outline of the so-called A. Gray ana ; 

 indeed, so much so, that it might pass for it, if the description 

 and size did not somewhat differ ; but notwithstanding this dis- 

 crepancy, I almost think tlie figure (the outline size having 

 perhaps being accidentally omitted) may l^e intended to repre- 

 sent our Truncatella Gray ana. 



These extracts show that Dr. Gray's conchological generic cha- 



