460 Mr. J. Alder on Jeffreysia and Cheninitzia. 



XLV. — On the distinctive Characters of Jeffi-eysia and Chem- 

 nitzia. By Joshua Alder, Esq. 



To Richard Taylor, Esq. 

 Dear Sir, 

 In my last letter ou the subject of Jeffreysia, I endeavoured to 

 draw up as clearly as possible the true characters of that genus 

 and of Chemnitzia, in order to show the impossibility of their 

 being considered the same. Mr. Clark has replied to this state- 

 ment ; at first rather doubtfully, so far as Jeffreysia opalina* is 

 concerned, but gaining confidence as he proceeds, he at last be- 

 comes 'irrevocably' satisfied with the correctness of his own 

 r"^nions. In a subsequent paper that gentleman takes the op- 

 portunity of re-asserting those opinions, and makes some obser- 

 vations on Professor Loven's account of Chemnitzia {Turbonilla), 

 into the correctness of which it will be necessary to examine. 

 The objections brought forward against my statement are: — 

 first, that the operculum affords a very inconstant character, 

 varying from annular to spiral in the same genus, and even in 

 different individuals of the same species ; and that, secondly, the 

 operculum of Chemnitzia has an apophysis. With respect to 

 the animal itself, I have endeavom-ed to glean the ' host of facts' 

 that are stated to be brought forward, but all I can find is that 

 there is a similarity of position in the eyes of the two genera, 

 and that this position of the eyes is not to be found in any of 

 the Litturinidce. For the characters of the head we are refeiTcd 

 to Philippi. 



As to the variable nature of the operculum in the same genus 

 or species, I can only say that such is contraiy to my experience. 

 It is not asserted that any variation takes place in the operculum 

 of Jeffreysia, excepting the occurrence of a double apophysis 

 in some specimens of /. opalina, a circumstance that I have ob- 

 served, but which appears to be a splitting of the process into 

 two lairs, or at most it can only be considered a lusus. The 

 typical character still remains the same. In Chemnitzia however 

 the operculum is stated to vary more, but we do not find it said 

 that it departs from its subspiral character, unless it be in C. rufa, 

 where we are informed that " a part of the area is coarsely an- 

 nular, with strise on the other part radiating from the elliptic 

 curves." That is, the operculum is half annular and half spiral. 

 I do not possess the species alluded to, at least the one so called 

 by Mr. Clark in his last paper, but I may be allowed to express 

 a doubt that the supposed annular portion has been con*ectly 



* Living specimens of this interesting moUusk have been kincUy forwarded 

 to me by my friend, Mr. Barlee, from «hich I am aljle to confirm the ge- 

 neral accuracy of Mr. Clark's description, though I entirely dissent from 

 his conclusions. 



