192 LINEUS BILINEATUS. 



Habitat. — Generally occurs in somewhat deep water on coralline ground, or oyster-beds, 

 but also under stones and in cracks of oyster-shells between tide-marks. The largest specimen 

 I have seen was procured from the stomach of a haddock caught off St. Andrews Bay. 



Body. — A few inches to a foot and a half in length, and of variable breadth ; not much 

 flattened, except on the ventral surface, widest in front and gently tapering towards the pos- 

 terior extremity. 



Colour. — Various shades of pale madder-brown, chocolate or reddish-brown, darkest in 

 front, and gradually fading posteriorly. Prom the centre of the snout, just within the pale border, 

 a white or yellowish stripe commences by a wide origin, which occupies nearly the whole breadth 

 of the region, and proceeds to the tip of the tail along the middle line of the dorsum. It is 

 widest anteriorly, and is rendered double by a dark central streak. Sometimes a young 

 specimen presents an opaque white pigment-patch on each side of the usual central bands of the 

 snout, so that by transmitted light the organ seems furnished with two large eyes. In a variety 

 the anterior third was very pale, the rest of the body being of a bright rose or carmine colour. 

 The under surface of the body is paler than the upper, especially towards the middle line and the 

 region of the mouth. Specimens found in exposed places between tide-marks are darker than 

 those from more sequestered regions. 



Head. — Flattened and somewhat spathulate, rather blunt anteriorly and.somewhat narrowed 

 posteriorly at the termination of the .cephalic fissures, from which a slight depression slants 

 inwards and backwards towards the central stripes. The lateral fissures are deep, and tinted of 

 a vivid red colour towards the pit posteriorly. The narrowing of the snout anteriorly and poste- 

 riorly gives it a somewhat elliptical or ovoid appearance. There is no trace of eyes or eye-specks. 

 The mouth opens a short distance behind the ganglia. 



L. bilineatus is rather a sluggish species in confinement, but is easily preserved alive for 

 years. It progresses with a rolling motion of the head, but will remain for weeks in a 

 dormant condition under a shell or in a mass of hardened mucus. The skin is strongly acid to 

 test-paper. 



I have not found specimens containing developed generative organs, but Sir J. Dalyell 

 relates of his captives that a vast quantity of white ova, amidst a thin glairy matter, appeared in 

 the vessel in June. 



I have little doubt the Folia bilineata of Delle Chiaje refers to this species ; and since he 

 describes the Cerebratulus (Opkiocephalus) bilineatus of Renier as quite a different form, probably 

 the same as the Nemertes peronea of De Quatrefages, with two dorsal black lines, I have 

 omitted Renier's name altogether from the synonyms, for I have not been successful in seeing a 

 copy of his early work. It is unlikely that so acute an observer as Delle Chiaje would confound 

 the two species, especially as the published description of the first form was in his own language. 

 Sir J. Dalyell thought the Planaria dorsalis of Abildgaard (Tetrastemma dorsalis) was pro- 

 bably a mutilated fragment of this worm. M. van Beneden, again, not long ago described it 

 as a new species from deep water off the Belgian coast. I have not been able to verify this 

 author's remark, that there are three divisions in the alimentary canal, nor have I ever seen it 

 or any other Nemertean " threatening its prey with its proboscis." In his c Nachtrage zur Revision 

 der Turbellarien' Diesing erroneously places Dalyell's Gordius tcenia (the present form) under 

 Omniatoplea jperonea. 



