20 Prof. M'Intosli's Notes from the 



and backward. The tentacles are numerous, and liave tl.e 

 median groove so characteristic of such organs. Ventrally 

 tlie dorsal collar terminates, in spirit-preparations, in a short 

 edge. 



The body is enlarged in front, though in the small speci- 

 mens this is slightly marked, and tapers to a moderately 

 slender tail, at the tip of which is the anus. The segments 

 vary from forty to fifty-five. The dorsal surface is rounded, 

 the ventral with thirteen shields in front, and the median 

 line thereafter is marked by a deep groove. 



The branchise are two in number, and vary much according 

 to the age of the specimen, young forms having only short 

 stalks without divisions, whereas adults have the branchiie 

 well developed and more or less dichotomously divided — with 

 short terminal branches. The anterior gill is the larger. 

 All intermediate forms occur between the one stage and the 

 other. The best-developed branchiae occur in those from 

 deep water, e. g. 80 fathoms off North Unst, Shetland, the 

 first pair having a comparatively long stalk before splitting 

 into the terminal tul't. The disj)roportion between this and 

 the second pair is marked, the latter being a short process 

 with only a few divisions. 



On each side are fifteen bristle-bundles, consisting of 

 translucent bristles wiih shafts which slightly diminish 

 toward the upper end, where the narrow wings commence 

 and continue on the somewhat long and finely tapered tips 

 for a considerable distance, disappearing, however, on the 

 hair-like extremity. The tufts difl'er, e*. g. from those of 

 Amphitrite gracilis, in being single, no shorter series 

 occurring as in other types. The first bristle-bundle occurs 

 behind the second branchia, and it has no apical appendage, 

 but the two following have on the doisal side of the seti- 

 gerous process, and continuous with it, a lanceolate process 

 like the branchia of Ai'icia. 



The hooks present a single tooth above the main fang, 

 though in some traces of a second appear in lateral view. 

 The base is somewhat small in proportion to the crown and 

 neck, and its lower edge is evenly convex. The process on 

 the anterior edge curves upward, so as to make a narrow 

 gulf below the great fang, and the edge beneath it is 

 concave. The posterior or dorsal edge has only a slight 

 indentation before joining the base. A series of striations 

 pass from the crown down the posterior part of the neck. 



In the widely-distributed Pista cristata, O. F. Miiller, the 

 eleventh species, the cephalic plate has a thick dorsal collar 



