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IV. On the Anatomy of Doridopsis, a Genus of the Nudibranchiate Mollusca. 
By ALBANY HANCOCK, F.L.S. 
(Plates XV.-XX.). 
Read January 19th, 1865. : 
- DORIDOPSIS has until lately * been confounded with Doris, which, indeed, it very 
closely resembles,—though it may always be distinguished by the position and character - 
of its mouth, and generally by the softness of its dermal envelope, which is devoid of 
spicules, granules, or any other calcareous bodies whatsoever. It is also usually more 
elongated, with the sides parallel, and is frequently vividly coloured. Six or seven 
species have been described, all from Madras t. A castaneous species also occurs in 
Madeira. They divide themselves naturally into two principal groups, one of which is 
characterized by the smoothness of the mantle, the other by its being covered with soft, 
warty tubercles. 
. The species mainly relied upon on this occasion belongs to the latter division, and has 
been named D. gemmacea. It is three or four inches long, and is rather narrow in pro- 
portion to its length, with the mantle covering the head and foot, the latter projecting 
only a little behind when the animal is moving. The pallial tubercles are compound, 
and are placed symmetrically in three rows along the back and sides, with smooth 
lozenge-shaped spaces between them. The head is inconspicuous, bulging forward a 
little in front of the anterior margin of the foot, and having the sides produced into 
short angular points. The mouth is in the form of a small circular aperture, placed a 
little baekward in a depression or cleft in the thickened margin of the foôt. The dorsal 
tentacles are retractile within cavities, are placed well forward, and are clavate, with the 
upper portion laminated. There are five retractile branchial plumes, which are quadri- 
pinnate; they are placed towards the posterior extremity of the middle line of the back, 
surrounding the anal nipple and renal orifice. The genital opening is placed well 
forward, on the right side, between the mantle and foot. The foot is rounded at both 
extremities, a little more abruptly in front than behind, where it projects slightly beyond 
the mantle when the animal is crawling. In front, the margin is thickened and cleft in 
{he centre, the mouth-opening in the cleft; in some species a little behind it, where there 
à smooth area extending from side to side, and bounded backward by a ridge which 
indicates, apparently, the true margin of the foot, the thickened margin in front being 
tle representative of the anterior lamina in Doris. (Pl. XV. fig. 3, and PL XX. figs. 3 & 4.) 
Though this species is stated to be three or four inches long, the spirit-specimens dis- 
ected were scarcely more than one inch and a half in length. 
* Tt was described in 1863 by Messrs, Alder and Hancock, in a paper on Madras Nudibranchs in the ‘ Transactions 
t 
of the Zool, Soc.’ vol, v. p. 124. Ibid. 
VOL, XXV, 2D 
