102 On the genus Onchidium. [No. 2, 



places, and the correct position of the sexual opening is indicated 

 by the first portion of the external vas deferens. In the view of O. 

 marmoratum, the vas deferens begins at the place where the pul- 

 monary orifice is situated, which is no doubt a small error. None 

 of the other figured species which have been referred to OncMdella, 

 appear to me to add anything in support of a generic distinction, and 

 thus I think that a very strong reason exists to withdraw both the 

 generic names, Peronia and OncMdella, and refer the respective species 

 to Onchidium. 



The only other closely allied genus which belongs to the family 

 Oxchidiidje is Vagimdus (Veronicetta apud H. and A. Adams). Mr. 

 W. Theobald, Junr., described one species from Burma, V. JSirmanicus, 

 and my friend, Mr. Gr. Nevill, lately obtained near Calcutta two 

 specimens which appear to belong to the same species. I hope to 

 return to this subject as soon as I am able to procure better live 

 specimens of our own and the Burmese forms. 



Description of Bengcd species. 



1. Onchidium typhse, Buch., 1800. Pi. xiv, Figs. 1—5. 



Body during the motion of the animal much elongated and 

 narrow, rather convex, anteriorly and posteriorly obtusely round- 

 ed ; mantle above greenish, of various shades, covered with very 

 numerous smaller and larger tubercles, which are nearly equally 

 distributed over the whole upper surface. The smaller tubercles vary 

 a little in their size, but the larger ones have pretty nearly the same 

 dimensions, those about the centre of the back being slightly higher 

 than others. These tubercles are at their bases and at the sides some- 

 what darker than the body, the top being, however, usually paler and 

 provided with from 1 — 4 jet-black clots. None of the tubercles are 

 permanent, they can be, in the live animal, always retracted in the skin 

 which is rather tough. 



The head is of considerable size, dark greyish, in front covered with 

 numerous, rather large whitish warts ; the buccal appendages are 

 blackish, with their front edges and the tentacles yellowish green ; 

 the pedicles are thick, concentrically roughly wrinkled, slightly bluish, 

 transparent at their base, greenish for the greater part of their length, 

 pale near the tips, where the small black eyes are situated. The 



