272 Mr. W. Clark on the Genus Assiminia. 



XXV. — Observations on the Genus Assiminia. 

 By William Clark, Esq. 



To the Editors of the Annals of Natural History. 



Gentlemen, Norfolk Crescent, Bath, Sept. 11, 1856, 



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, " jMr. 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 off 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, Avith a w^hite 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 ' Enumei'atio Molluscorum 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, ajnce demum decollatas, globoso-conoideas, 

 imo discoideas. Illi quibus banc ob causam nomen TruncatelUe 

 uon placet, nomine Churistoma a Dc Cristophoris ct Jan pro- 

 posito utantur, ne novo nonjiue scientiam jam nominibus gra- 

 vatam onerent." 



And Phibpj)! illustrates these views by four figures, tab. 24-. 

 f. 2, 3, 4, 5 ; three of them difi^'er 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 the figure (the outline size having 

 perliaj)s being accidentally omitletl) may be intended to repre- 

 sent our Truncatella Gray ana. 



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



