1869.] On the genus Oncliidium. 101 



granules. I had myself no opportunity of examining any of the 

 forms called Peronia, but from the numerous variations in the external 

 appearance of the tubercles, which I have observed in our species (as 

 for instance in 0. tenerum) I cannot perceive how this character 

 could be considered as of any generic value. Besides that, the authors 

 who acknowledge, upon this ground, the generic distinction of Teronia, 

 are far from consistent in dealing with the question, for they refer 

 to Onchidella species which are either smooth or granular, some of them 

 being very coarsely granular, and even spinous above. Surely, the dis- 

 tinction between a smooth and granular or tubercular surface is greater 

 than that between the latter and one in which the tubercles bear two or 

 three points in place of only one. The presence of two or three 

 black dots on some of the large tubercles of Oncliidium typlice appears 

 to me to be fully equivalent to some of the tufts observed in Oncliidium 

 Peronii, and very likely in very old specimens these black dots may 

 become pediculated, for I have myself observed them each raised in- 

 dependently from the other. I must here specially call attention to 

 some of the variations in the mantle surface of Onch. tenerum, 

 described towards the end of this paper. 



Gray proposed for Lesson's species, Onch. granulosum, the name 

 Onchidella, and referred to this presumed genus all the granular or 

 smooth species, except Oncliidium typhcd. In what the distinction of 

 Onchidium and Onchidella ought to consist, I entirely fail to perceive. 

 H. and A. Adams in their " Genera of Shells," II. p. 232, state that 

 the latter differs from the former in having the buccal appendages 

 lobate, but then they say exactly the same of Oncliidium. I am not 

 quite certain about the meaning of the word lohate with regard to the 

 buccal appendages, but I think it can only refer to the thickened rims, 

 which I explained as the tentacles and which, with reference to the 

 front edges of the appendages, may be called lobes. Wherefrom H. 

 and A. Adams derived the statement regarding the position of the 

 pulmonary orifice " at the right side under the mantle," does not 

 appear evident. 



Lesson's figures of the ventral views of Onch. granulosum and 

 marmoratum do not in the least support any generic distinction 

 among the species described as Onchidium. In the former the 

 anal and the respiratory orifices are marked in their proper 



