LINEUS GESSERENSIS. 187 



1865. Borlasia olivacea, Johnston. Catalogue Brit. Mus., pp. 21 and 289, pi. lib, f. 1 and 1*. 

 „ ,, gesserensis, Ibid. Op. cit., pp. 21 and 290. 



y , Lineus viridis, Jbid. Op. cit., pp. 27 and 296. 



1866. Borlasia olivacea, Lankester. Ann. Nat. Hist., 3rd ser., vol. xviii, p. 388. 



1867. „ „ Mcintosh. Jour. Micros. Sc. ; Trans., p. 39. 



1868. „ „ Ibid. Ann. Nat. Hist., 4th ser., vol. ii, p. 293. 



1869. „ „ Ibid. Trans. Roy. Soc. Edinb., vol. xxv, pt. ii, p. 371 et seq. 



Habitat. — Abundant on all our shores under stones between tide-marks, and in the laminarian 

 region, from the Shetland to the Channel Islands. 



Body. — Pour to nine inches in length, breadth a line and a half or more, flattened, tapered 

 towards the head, and more distinctly towards the tail ; marked by numerous pale transverse 

 wrinkles, somewhat regularly disposed, and most conspicuous in pale specimens. 



Colour. — Two very distinct hues are characteristic of this species, viz. reddish-brown and 

 dull olive, while pale reddish and green varieties are also occasionally met with. The pigment is 

 generally darkest in front, before and behind the reddish mark in the ganglionic region, the rest 

 of the body being uniformly tinted except towards the tail, which is paler. The snout is sur- 

 rounded by a broad pale margin, as far back as the termination of the fissures. The ciliation 

 gives the body under certain conditions either a purplish or an opalescent hue. The sides are often 

 marked with numerous pale spots, from the generative apertures. The ventral surface is paler 

 than the dorsal, especially towards the snout, which is also reddish posteriorly. The mouth is 

 surrounded by a pale margin. Party-coloured varieties are sometimes found, the anterior region, 

 for instance, being dark green mottled with white, while the posterior half is quite pale. Such 

 bleaching is different from that caused by parasitic attacks. 



Head. — Somewhat elongated, flattened, spathulate, rather truncate in front, with a small 

 central and two lateral papillae, and having on each side — from the tip of the snout backwards — 

 a deep fissure with pale edges and a pinkish bottom, the latter hue being most distinct posteriorly. 

 It tapers slightly anteriorly, and is decidedly wider than the succeeding portion of the body, on 

 account of the lips of the lateral fissures. The eyes are situated at the anterior central pig- 

 mentary portion of the snout, and number from three to six or more on each side, the largest 

 being generally in front. They are not always symmetrical ; three, for example, occurring on one 

 side, and occasionally eight on the other, besides some indistinct grains. The mouth opens as a 

 longitudinal slit a short distance behind the ganglia. 



L. gesserensis progresses in an easy, graceful manner, with slight undulatory motions of the 

 head, its body being marked with successive contractile waves, which proceed from before back- 

 wards. The specimens frequently herd together in the water, which they are prone to leave, 

 and remain attached to the side of the glass a considerable time. They are very easily kept in 

 confinement for years ; but, as with many of their allies, great diminution of bulk occurs, from 

 deprivation of the natural supply of food. When recently captured specimens are placed in a 

 jar containing injured Annelida, numerous faecal masses, consisting of the bristles of Nereis 

 pelagica, and other annelids and digested matter, are found lying on the bottom of the vessel, 

 showing how greedily they have fed ; a fact, indeed, very easily ascertained by actual observation. 

 It is also frequently noticed that specimens confined in vessels along with the deep green 

 Eulalia viridis assume a similar hue, probably from feeding on the rejected debris of those 

 animals, if not upon the latter themselves. In their native haunts the stones under which they lie 



