104 On the -genus Onchidium. [No. 2, 



body. The entire surface is almost equally granular, with a small 

 number of more or less regularly distributed larger tubercles, each 

 provided with one, seldom two black dots. The larger tubercles were 

 in one specimen arranged in two longitudinal rows on either side of 

 the dorsal stripe, but in other specimens, they were irregularly placed. 

 The black central stripe is widest in the middle, with a pale spot in 

 the centre in which are situated three black dots ; these being only 

 observable in large specimens. The edges of the mantle are slightly 

 thickened ; its colour below being of the same, uniform, pale yellowish 

 white hue, as above. The foot is obtusely pointed posteriorly- and 

 truncate in front ; it is greyish yellow, varying in tints according 

 to its expansion and consequent transparency ; the colour of the internal 

 organs is traceable through it. 



The head and eye-pedicles are dark, with a distinct greenish tinge ; 

 the mantle and the buccal appendages paler ; the front edges of the 

 latter and the tentacles pale yellowish green. The length of the 

 pedicles is generally less than half an inch, and they are somewhat 

 thinner than in the previous species ; the eyes are black. 



The anus lies at the end of the foot ; the pulmonary orifice just 

 behind it, being rather small and surrounded by thickened margins. 

 The hermaphrodite genital pore lies to the right, quite close to the 

 anus ; the external vas deferens enters the body on the side below 

 the right buccal appendage, and the penis opening is situated in front, 

 below the right pedicle. Young specimens are paler in colour than 

 • old ones, and the dorsal stripe becomes occasionally rather indistinct. 



The disposition of the internal organs entirely agrees Avith the 

 type species, Onchidium typhce. The internal vas deferens is fully 

 four inches long ; the supplementary albuminous string, near the 

 penis, is about 5 inches long, much shorter than in the previous 

 species, but thicker in front ; the liver at the end of the stomach 

 is a large, dendritic gland ; the receptaculum seminis is very large 

 and folded ; uterus thick and twisted, and like the small albu- 

 minous gland and the testis pure white ; the large albuminous gland 

 is purple or rose-coloured, the folicles being filled with a granular 

 substance, which has the appearance of undeveloped eggs. The ova- 

 rium is deep yellow, containing large oval eggs. The cardial cavity 

 extends to nearly half the length of the body, but the heart itself 



