340 Mr. Alder on the Genus Polycera. 



b. With 4 branchial appendages, body with spicule. 



P. citrina, n. s. Plate IX. fig. 7 — 9. 



P. minute, lemon-yellow, with 5 rows of tubercles down the back. 

 Veil surrounded with numerous small tubercles, 5 branchial plumes, 

 and 2 pair of short branchial lobes. 



Body limaciform, prismatic, about 2 lines long, rounded in front, 

 tapering to a point behind, pale lemon yellow, studded with five 

 rows of tubercles of a deeper shade of the same colour. Tentacula 

 two, short, broad, and strongly imbricated, behind which are two 

 very minute eyes. Veil strongly sinuated in front, and rounded at 

 the sides, the margin divided into 12 or 14 short tubercular expan- 

 sions ; from the sides of the veil an elevated ridge, studded with 

 tubercles and capable of a slight expansion, runs along each side of 

 the back, uniting behind the branchial lobes and extending in a 

 strongly tuberculated keel to the tail. Branchial plumes about five, 

 transparent, forming a semicircle in front of the vent, a little behind 

 which are four short, opake, rounded branchial lobes, two on each 

 side. Mouth without tentacula. Foot linear, a little expanded and 

 angulated in front. Body containing imbedded spiculse. 



A single specimen was found on a coralline from deep water 

 in a fishing boat at Cullercoates. 



When put into a watch-glass of sea water, so fond was this 

 little creature of swimming inverted on the surface (a treat 

 which one would think it could scarcely have in its natural 

 place of abode), that it could with difficulty be made to remain 

 at the bottom a sufficient time to allow of a drawdng being 

 made of it. 



The Triopa Nothus of Johnston is probably a Polycera of 

 this division. 



c. With 10 branchial appendages, without veil or spicules. 



P. cristata, n. s. Plate IX. fig. 10, 11. 



P. smooth, white, without veil, with 2 pair of tentacular filaments, 

 3 plumose branchiae, and 10 branchial appendages. 



Body nearly half an inch long, limaciform, of a transparent watery 

 white, smooth. Tentacula two, large, club-shaped, pale yellow, not 

 retractile, strongly imbricated on the upper part and terminated by 

 a mucro ; from the bases of these spring two pair of simple, linear, 

 tentacular filaments tipped with bright orange, and also non-retract- 

 ile ; two inferior tentacular processes are situated at the sides of the 

 mouth, capable of considerable extension and contraction. No eyes ? 

 The vent is in the centre of the back rather nearer the posterior end, 

 and is surrounded by three beautifully plumose, transparent white 



to have a quickness of pulsation quite unexpected. In Vitrina pellucida, 

 for instance, 1 have found the heart to beat so many as 120 times in a mi- 

 nute, while in other states of the same animal the pulsations have been 

 very slow, and sometimes suspended for several seconds. 



