106 On the genus Onchidium. [No. 2, 



fresh and very large specimens ; when they are kept for only a short 

 time, all the fine spines are retracted in the mantle. 



The colour is above pale green with numerous blackish, irregular 

 spots, which are generally more numerous about the centre of the back 

 and at the edges of the mantle, than between both. Young specimens 

 are more uniformly coloured. In the old ones, the green colour is some- 

 times rather dark, so as to make the spots less conspicuous ; in others 

 there is a distinct blackish green irregular stripe along the centre of the 

 back, of about the same length as the foot ; two similar blackish stripes 

 originate one behind each of the pedicles, running a short distance from 

 it more or less paraRel to the dorsal stripe, till all three join near the 

 posterior end. Both the central and the lateral stripes are not con- 

 tinuous, they are moreover formed by the spots becoming more or 

 less confluent. Young specimens have the mantle below uniform, 

 light bluish with very numerous and minute white dots ; large ones 

 have occasionally a number of dark green or rusty, more or less con- 

 fluent spots along the lateral margins, and the general colour is paler. 

 The foot is comparatively narrow, about one-third of the width of the 

 body and when contracted about one-fourth only ; it is of a uniform 

 dark bluish grey colour, sub-truncate anteriorly and rounded or 

 obtusely pointed posteriorly, with the edges free and sharpened all 

 round. 



The head and the pedicles are dark green, the latter far apart, 

 thick at the base, very thin in the middle, with slightly thickened 

 tips which bear the black eyes at their upper surface. The buc- 

 cal appendages are of moderate size, blackish, with greenish grey 

 front edges, and the tentacular rims yellowish green. The male 

 genital pore is very distinct, situated in front at the base of the right 

 pedicle ; the anus and the pulmonary orifice are normal, the herma- 

 phrodite opening about Jth of an inch distant to the right of the 

 anus, elongated, and surrounded with swollen lips ; the external vas 

 deferens enters the body below the right buccal appendage, but very 

 close to the lips of the mouth, passing obliquely through the tissue 

 towards the male genital pore. 



All the internal organs agree with the type species. Thel 

 ovarium is small, orange yellow ; the testis, and its supplemen- 

 tary gland, white, the albuminous gland and the uterus pale 



