1901.] SOME AECTIO NEMERTEANS. 91 



Tu the following paper I have first given an account of the new 

 species, and have added at the end some notes on such points of 

 more general interest as have arisen in connection with them. 



'MBTAIfEMEETIlfl. 



Amphiporus thompsoni, n. sp. (Plate VI. fig. 6 & Plate VII. 

 fig. 8.) 



Xumerous examples from three localities, i. e. N. Greenland 

 (collected by Herr Lohmaun), "Upernavik, and Davis Strait. 

 Isf. Average length about 50 mm., with a breadth of 3 mm. when 

 not greatly contracted. Body rounded and tapering at either end. 

 One very large specimen measured 120 mm. in length and 6 mm. 

 in breadth. Colour dorsally reddish brown, ventrally pale 

 yellowish buff, probably white in life. A darker streak occurs on 

 the snout dorsally (Plate VI. fig. 6), and behind this there are two 

 transverse white lines marking the position of the head-furrows. 



The epithelium, which is devoid of unicellular glands, rests on 

 a basement-meinbrane of about one-half its thickness. In the 

 head-region the basement-membrane is pierced by numerous small 

 nerves. The muscular system is of the usual type. The circular 

 muscle-layer is of about one-third the thickness of the basement- 

 membrane (i. e. about 20 p.). The longitudinal layer is about 5 

 times as thick as the circular. Dorso-ventral muscle-strands 

 occur in the oesophageal and intestinal regions. The vascular 

 system shows a •well-marked cephalic loop. The limbs of this loop 

 converge to pass through the nervous ring, and as they lie upon 

 the ventral commissure the median dorsal vessel is given off from 

 either the right or the left, and not from both as is usually the case 

 where a median dorsal vessel exists. A similar arrangement was 

 observed by Dr. Willey in a small Amphiporid from New Britain. 



Text-fig. 1. 



median dorsal 

 vessel 



cephalic loop 



_uun 



Diagram of anterior part of vascular system of Amphiporus thompsoni. 

 (For explanation, see text.) 



In the oesophageal region of A. thompsoni, where the excretory 

 tubules are present, the lateral vessels give off dorsal branches 

 which are united by a longitudinal vessel running for a short 

 distance along the side of the proboscis-sheath (vide text-fig. 1). 

 The dorsal blood-vessel Leaves the proboscis-sheath very soon after 

 the brain ends, and before the level of the excretory pore 

 (Plate VII. fig. 8»). 



1 The classification given in Burger 1 ! Bloaograph (1895) has been followed, 



