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REPORT ON THE NUDIBRANCHIATA. 
(which is not co-extensive with Gray’s Onchidella ) ; whether this generic distinction can 
really be made must be left doubtful for the present. 
The Onchidiadse unite the characters of the Steganobranchiata, the Nudibranchiata, 
and the Stylommatophorous Pulmonata. They are, like the first two groups, generally 
marine. In having a ciliated furrow on the right side, they resemble the Steganobranchiata. 
In the general form of the body they are not unlike Doris. The central nervous system 
closely resembles that of the Pulmonata ; still, the pedal ganglia are separated, as in the 
Nudibranchs ; and the retractors of the rhinophoria also resemble those of this latter group. 
They are, however, more especially related to the Stylommatophorous Pulmonata , like 
them possessing rhinophoria (Ophthalmophoria) and a foot gland. In spite of its 
modification, the nervous system is fundamentally similar, the gastro-cesophageal ganglia 
being also absent. They have also the uropulmonary system of the Pulmonata, and 
resemble them further in the structure of the genital system ; a spermatocyst is always 
absent. The blood gland, so commonly present in the Doridicke, is also absent. 
With regard to the phylogenetic development of the Onchidiaclee, it seems likely that 
they have really nothing to do with the Nudibranchiata. A number of intermediate 
forms, however, connect them with the Pulmonata, and it seems more reasonable to 
suppose that they descend from the Stylommatophorous Pulmonata (Nephropneusta, v. 
Jhering), with which group they agree so closely in anatomical structure, and from which 
they do not deviate too much in development. They seem, in short, to be Pulmonata 
which have become adapted to an amphibious or marine life . 1 
Onchidium, Buchanan. 
Onchidium melanopneumon, n. sp. (PI. IV. figs. 25-27; PI. V. figs. 1-27; PI. VI. 
figs. 5-18, 20, 21). 
Species Onchidio tongano magnopere affinis, colore dorsi obscuro (atro vel caeruleo- 
atro V), pulmone aterrimo. 
Habitat. — Pacific (Fiji Islands). 
Only one specimen was taken in shallow water at Kandavu, in the Fiji Islands, August 
1874, and was preserved in alcohol. The length of the animal was 6'5 cm., its breadth 
4 cm., and its height 2’5 cm.; the breadth of the mantle edge about 1 cm., of the foot 
about 2T cm.; the free anterior margin of the foot projects about 4 mm., the tail is 6 mm. 
long, the head 17 mm. broad, the length of the rhinophoria 5 mm., the diam. of the 
pueumostome-papilla 5’ 5 mm. 
1 Brock, in his critical review of the memoir of J. Joyeux Laffuie (Biolog. Centralhlatt., Bel. iii., 12, 1883, p. 370-374), 
regards the Onchidia.as Nudibranchiata, allied to them by their organisation as well as by ontogeny. The Memoir of 
Dr. Brock did not come to hand before this sheet had been printed, but I still regard his opinion as erroneous. 
(ZOOL. CHALL. EXP.— PART XXVI. 1884.) Cc 17 
