166 TETRASTEMMA ROBERTIAK.E. 



The pairs are equidistant. Rarely the single specks are represented by two or three smaller 

 pigment-patches. 



Cephalic furrows, — An oblique furrow runs from the margin on each side inwards and 

 backwards towards the posterior eye, and behind the latter two other grooves meet at an angle, 

 as in A. lactifloreus, in the middle line of the dorsum. On the under surface of the snout a 

 furrow passes from the cephalic pit inwards on each side ; and there is a continuation of the 

 posterior furrows, as in the last-mentioned form. 



It is less hardy than A. lactifloreus in confinement, but can readily be kept several 

 months. It remains chiefly at the water-line in a silky sheath of the tough transparent mucus. 

 Almost every specimen in the free state in the Channel Islands was furnished path the latter, 

 though the case was less transparent on account of the adherent debris. The skin gives an acid 

 reaction to test-paper. 



I have not yet seen a specimen of this species with ova or spermatozoa, so that it must breed 

 very late or very early. The young soon acquire the black patch on the snout, and other 

 characteristics. It was absent from the rocks at St. Andrews in April and May. 



This species was first discriminated by Col. Montagu under the name Planaria unipunc- 

 tata, though Dr. Johnston's title has the priority by publication. The former described the 

 species, which he procured on the south coast of Devonshire, as follows : — " Body filiform, with a 

 black subquadrangular spot that nearly covers the head, behind which are two minute black eyes, 

 distant from each other." The Planaria ascaridea of the same author had the " body long, 

 linear, white, with a square black spot close to the anterior end," and in all probability is to 

 be referred to the same species. Length one inch. Moreover, though he describes the square 

 black spot of Planaria filum as situated between the pairs of eyes, this too can scarcely be any 

 other animal than that now under discussion. (Ersted remarks that there is a transverse 

 brown bar between the eyes of his Tetrastemma rufescens, but there is no other character 

 to connect it with this form. It is probable Professor Kolliker refers to the same species 

 under the name Nemertes Knochii (Krohnii?), as he describes a transverse brownish-red band of 

 pigment on the head. There is no doubt of the identity of the present species with the Polia 

 coronata of M. de Quatrefages, from Brehat, though his figure of the head is faulty, and the 

 colour peculiar, since he states that the spot between the eyes has a violet hue. The Polia 

 pulchella of the same author, from Sicily, seems to be a greenish variety, in which the pigment- 

 patch on the head is separated from the eyes in front and behind by a larger interval than 

 usual. 



2. Tetrastemma eobertiais 1 ^, n. s. Plate III, fig 1. 



Specific character. — Anterior pair of eyes larger than the posterior, which are sometimes 

 quite hidden in 'the pigment-belt; body longitudinally striped with two brown and a median 

 white line. 



Habitat, — Dredged in four fathoms in Lochmaddy amongst tangles, and from the roots of 

 the same seaweeds in Bressay Sound at a depth of six to eight fathoms. 



Body about l|th inch long, flattened, rather narrowed in front, then gently dilating towards 

 the tail, which is slightly tapered, and furnished with a somewhat thin margin. 



