Gatty Marine Laboratory, St. Andrews. 41 



posterior edge only with five or six small teeth in lateral 

 view (and which do not affect tlie straight outline of the 

 crown) in contrast with the four large teeth of the British 

 form^ which project well over the main fang, and the striae 

 from which occupy a considerable portion of the neck ; and 

 the strise adjoining these (in front) are parallel, whereas 

 in the arctic hook the long striae from the smaller hooks on 

 the crown are indistinct, the striae in front being alone 

 conspicuous. The posterior outline in the two hooks like- 

 wise differs, the arctic form being evenly convex till near 

 the base, where it is truncated, the British having this 

 portion of the posterior edge concave. 



The distinctions noted continue posteriorly. Thus the 

 bristles near the tip of the tail in the British form, while 

 they have greatly elongated tips, retain the marked con- 

 striction of the shaft below the tip and the dilatation beyond 

 it. On the other hand, the extremely slender tips of C. in- 

 fundihuliformis have only a trace of wings, and the slight 

 constriction of the shaft below and dilatation above the 

 commencement of the wings would not at first sight be 

 noticed. The terminal hooks iji the British form have a 

 more regular posterior outline, but otherwise keep to the 

 type seen in front, the main fang and the teeth above it 

 being especially distinct. On the other hand, those of 

 C. infundibuliformis retain all the distinctive features 

 already mentioned, the minute teeth at the back of the 

 flattened crown being so indistinct as to suggest fusion. 



When the digestive tract is exposed, it presents anteriorly 

 prominent oral papillae and glandular organs on each side. 

 The anterior region of the tract is brownish in colour, 

 chitinous, and very friable, and after a short course it 

 merges into a rounded and more distinctly moniliform 

 portion, which, gradually diminishing in calibre, ends in a 

 small anus. The contents of the gut showed many diatoms, 

 fragments of the spicula of sponges, fragments of minute 

 Crustacea, amidst muddy sand. A large and firm glandular 

 body is attached to the intestine, and above the intestine 

 lies the dorsal blood-vessel, which has in the preparation a 

 brownish barred aspect. 



The anterior half of the intestine is of a pale brownish 

 hue and somewhat firm, as if chitinous, and in minute 

 structure is finely striated transversely, and hence the 

 readiness with which the gut ruptures. Few muscular 

 fibres occur in the anterior region of the gut, but at the 

 point where it becomes moniliform a layer of muscular 

 fibres lies beneath the chitinous coat, which becomes thiu 



