APPENDIX. 515 



are nothing more than the young conditions of Chiton asellus, 

 which varies much in the dimensions of its longitudinal and 

 transversal areas, as well as in the density and regularity of 

 the linear punctated sculpture. Or we must conclude that 

 these species are not in our collection, though we have been 

 assured by good conchologists that our shells represent them. 



Since writing the above we have dissected specimens of 

 both the so-called species, and found all the separate valves 

 finely crenulate, not emarginate ; thus confirming the opinion 

 that our shells are C. asellus. Therefore if Mr. Lowe's 

 C. aselloides the C. albus of authors is bi-emarginate on 

 each side the valves, it cannot belong to the present species. 

 It has however been suggested, that it may be a young, 

 white, finely granulated C. cinereus ; we should have con- 

 curred in this view if it had not been opposed to so accurate 

 an observer as Mr. Lowe. 



Our so-called C. cancellatus has the same finely crenulated 

 margins as C. asellus, which is, we believe, the only British 

 species thus sculptured. 



TROCHUS SERPULOIDES, p. 314; TR. CUTLERIANUS, p. 315 ; 



TR. NITENS, p. 316. 



Exmouth, 10th July, 1854. 



I have much satisfaction in stating, that the process under 

 the right tentaculum in these very minute species, which is 

 figured in a woodcut in the ' Annals of Natural History/ 

 vol. viii. p. 45, N.S., and styled " genitale" has not that func- 

 tion. I am the more pleased with this discovery, as no such 

 organ is to be found in that position in the large Trochi ; and 

 as these minute animals agree with their larger brethren in 

 all other respects, I was puzzled to account for this discre- 

 pancy. The difficulty is removed by finding that the process 

 I have alluded to is part of the right neck-lappet, which is 

 bifid ; both of its strands spring from the same membrane, as 

 I have seen clearly in a brilliantly transparent Trochus nitens 

 under high powers. The right neck-lappet is always longer 

 than the left, which however is also bifid, but plain, and 

 never ornamented, fringed or serrated, as is sometimes seen 



2 L 2 



