REPORT OR THE NUEIBRANCHIATA. 
19 
This new group is allied to the genus Janus, and resembles it in the outward form of 
the body, in the arrangement of the dorsal papillae, in the condition of the head, with its 
tentacles and rhinophoria, in the median position of the anal papilla on the posterior 
dorsal surface, and in the presence of the peculiar comb-like organ between the 
rhinophoria. 1 It differs, however, by the presence of a broad foot-brim, which probably 
assists the animal in swimming. This genus, however, is mainly distinguished by the 
enormous development of the mandibles, which, unlike what is found in Janus, form the 
sides of the bulbus ; the lower portion of the mandibles resembles that of Janus, but 
the masticatory edge differs in so far as it is not provided with denticles as in the 
typical Janus. The radula is like that of Janus; the median series of teeth weak, with 
rudimentary hook ; the lateral teeth numerous, with short recurved hook. In its 
internal structure the genus Janolus agrees on the whole pretty closely with Janus. 
The two genera belong to a special group, which includes also the Proctonotidm and 
the Madrellae. 2 Janolus differs from the Proctonotidse by the comb-like organ between 
the rhinophoria, and from the Madrellse, moreover, by the dorsal position of the anus, by 
the presence of special tentacles, and by the numerous lateral teeth on the radula. 
Only one species of this genus is known at present. 
Janolus australis, n. sp. (PI. VIII. figs. 15-22, PI. IX. figs. 6-8). 
Habitat.— Pacific (Arafura Sea). 
A single example of this species was taken in the Arafura Sea, during September 1874. 
The specimen was treated with picro-sulphuric acid, and preserved in alcohol. The dorsal 
papillae were nearly all wanting, but in other respects the animal was in good preservation. 
The length was 3 ’2 cm., the height 1 cm., and the breadth of the dorsal surface 11 mm., 
of the foot 17 mm. ; the breadth of that portion of the back which is beset with papillae 
at most 3 mm. The height of the rhinophoria quite 6 mm. ; the length of the tentacles 
4 mm. ; the height of the anal papilla 1’8 mm. ; the length of the tail 5 mm. 
The colour yellowish, but brownish or reddish along the middle line of the back ; the 
region between the rhinophoria and the inter-rhinophorial “ comb ” is covered with a black 
spot, and the extremities of the rhinophoria are also blackish. The form of the body is 
somewhat short and depressed ; the head flattened anteriorly, the mouth-opening perpen- 
dicular; the head is on every side produced into a rather narrow process, somewhat flattened 
below, which unites with the anterior edge of the foot and forms the upper lip of this 
anterior edge of the foot. 3 This wing-like process measures about 8 mm. in length, and is 
provided on its edge with a fine groove. The conical or finger-shaped tentacles take 
1 Gf. Bergh, Beitr. znr Kenntn. cl. iEolidiaden I., Verhandl. d. ic. lc. zool.-bot. Gesellsch. Wien., Bd. xxiii., 1873, 
pp. 597-605, Taf. vii. figs. 1-6, Taf. viii. fig. 1. 
2 Alder and Hancock, Notice of a collect, of Nudibr. Moll, made in India, Trans. Zool. Soc., vol. v. part 3, 1864, 
p. 141, pi. xxxiii. figs. 10-12. 
3 Cf. Bergli, loc. cit., 1873, Taf. vii. fig. 1. 
