294 Ml". W. Clark on the Clienmitzia opalhui (md C. diapliana. 



all these characters are occasionally subject to some modification. 

 We have several in our cabinet which differ materially, the an- 

 nular strise of increment being usually permanent ; the operculum 

 is carried rather posteriorly, not on a developed operculigerous 

 lobe ; the foot is not labiated so as to produce a meutum — at least 

 I saw none. The foot is not so slender proportionately as in the 

 typical Rissoa:, nor so long ; beneath it is pale yellow, showing a 

 medial line on the posterior half; above, elegantly mottled or 

 brindled with dark close-set lead-coloured lines, which are some- 

 times waved ; the colours on all parts vary in intensity in the dif- 

 ferent individuals. I could detect no head-lappets. These ani- 

 mals float and creep like the Chemnitzice and JRissua. Habitat ? 

 Mr. Barlee omitted to name it, but I presume it is in the lit- 

 toral and lamiuarian zones ; he has since confirmed this view. 

 Axis 2'oj diam. ^^ uncise. 



The muzzle of this animal allies it to Rissoa, and the peculiar 

 position of the eyes to Ckemnitzia ; further investigation is re- 

 quired to determine which is the most worthy character. I shall 

 soon have a good opportunity of entering on the examination of 

 these points. Notwithstanding the proboscidal muzzle not being 

 a strictly retractile one, I think the balance of characters is in 

 favour of this animal being a point of transition from the Litto- 

 rinidcE, and that it may be considered an aberrant Chemnitzia. 



With respect to Mr. Alder's strictures in the March 'Annals' 

 on my Chemnitzia diaphana, I am sorry that I cannot reply on 

 every point as I could wish until my return fi"om the sea-side. At 

 present I can only say, that the comparison of his so-called Jef- 

 fi-eysia with Chemnitzia is incorrect in most points, as I will show 

 hereafter. I think he will discover that he is in error respecting 

 the proboscidal apparatus of the Chemnitzice ; at least he is, if any 

 reliance can be placed on M. Philippics aiithorities. 



Mr. Alder has attached by far too great importance to the 

 modification of the striular form in the operculum of Chemnitzia 

 diapharui in comparison with those of the Chemnitziee, in which 

 they are very variable — not two are alike. Let him examine those 

 of the C. conoidea, C. pallida, and C. rufa ; indeed he will find 

 throughout the tribe that these appendages are very dissimilar ; 

 notwithstanding the variation in the shape of the opercular strise 

 in C. diaphana, I consider the operculum of that species of de- 

 cidedly Chemnitzian type, and that its characters ally it much 

 closer to the Muricidte, particularly to Murex undatus, than to 

 the Littorinida> — I mean, in the subannular form of the striae of 

 increment. 



Since the above was written I have again examined the animal 

 and shell of the Rissoa opalina, and I am bound to conclude, that 

 it is an aberrant Chemnitzia. The position of the eyes, far back 



