1869.J On the genus Onchidium. 105 



is only about fth of the length, distant from the posterior end. The 

 penis is about T 8 oth of an inch long, thick and strongly constricted 

 near the end, the flagellum being very short. 



The dentition (fig. Id) is similar to that of the last species, the 

 lateral teeth are rounded at the base with one large and one small in- 

 curved denticle. I counted about 150 cross series and about 500 

 teeth in each the formula thus being 250-1-250. 



The finely granular mantle with few scattered larger tubercles readily 

 distinguish this species from the previous, and the large quantity of 

 mucus which it secretes, has not been observed in any of the other 

 forms. The narrower form and greater convexity of the body are 

 equally characteristic distinctions between the present species and 

 O. tigrinum, n sp. 



The species was found at Port Canning, and appears to be rare. 

 I first obtained two large specimens through my friend Gr. Nevill. 

 Both had in front on the right side a small portion of the edge of the 

 foot detached (see fig. la), just on the place where the external vas de- 

 ferens turns towards the buccal appendages. This detached portion had 

 exactly the same structure as the rest of the foot disc, but whether it is 

 an accidental formation, or a normal one, assisting during the act of 

 copulation, I am not in a position to ascertain at the present. In 

 several small specimens which I subsequently obtained myself on the 

 banks of the Mutlah river, that particular detached piece was entirely 

 wanting. 



3.— Onchidium tigrinum, Stoi, Pi. xv, Fig. 2 



Body large, ovate, depressed ; mantle strongly coriaceous, hardened, 

 provided with sharp edges. The upper surface is entirely covered with 

 small granules, between which more or less numerous large elongated 

 tubercles are interspersed. Specimens of different sizes vary in this 

 point a great deal ; when young the tubercles are equally distributed 

 between the granules, being three or four times as large, and each 

 bearing a black dot at the tip, but being pale at the base. Old speci- 

 mens have either two or three irregular rows of large elongated tuber- 

 cles on each side of the back, or the larger tubercles are more numer- 

 ous, more equally distributed and spinulose, so as to give the surface 

 a very rough appearance. The latter stage is met with only in quite 



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