846 REPORT OF COMMISSIONER -OF FISH AND FISHERIES. [128] 



living, 10.5 mm . The last segment of this fragment was l.l mm long and 

 1.7 mm broad. The length of the head and neck in the living specimen 

 was 3.5 mm ; length of contractile bulbs l mm . 



Following are dimensions of the alcoholic specimen : Length of head 

 1,44mm breadth 1.66 mm ; length of bothria 1.60 inm , breadth 0.92 mm ; 

 length of head and neck, 3.14 mm ; diameter of neck, marginal, 1.10 111111 , 

 lateral l mm ; length of contractile bulbs 1.0S mm , breadth 0.26; dis- 

 tance from base of bulbs to first distinct segment, 3 mm ; length of first 

 distinct segment 0.1G ram , breadth 1.20 mm ; greatest breadth of seg- 

 ments 1.80 mm , length 0j60 mm ; lateral diameter behind bulbs, 0.90 mm ; 

 marginal diameter, 0.56 mm ; diameter of proboscides, 0.12 mm . 



The following description is based on the single alcoholic specimen: 

 Head broadly sagittate. Bothria two, oval, narrow in front, broad be- 

 hind, with thick, entire edges, a very faint emargi nation on posterior 

 edge, converging at apex of head, flaring posteriorly, so as to give 

 to the head the shape of an equilateral triangle. Neck a little 

 longer than head, swollen in front of contractile bulbs, fusiform on 

 account of contraction in length, slightly constricted at base of con- 

 tractile bulbs. Proboscis sheaths spiral, contractile bulbs four times 

 as long as broad. Proboscides longer than bothria; hooks of two prin- 

 cipal sizes, the larger ones stout, broad, aud strongly recurved, the 

 smaller ones also broad and strongly recurved, but some of them pro- 

 portionally more slender than the larger ones, a few slender and arcu- 

 ate. Larger hooks on outer side of proboscides, smaller ones on inner 

 side. First segments very short and broad; succeeding segments also 

 short and broad, with rounded margins; margins of segmented part 

 of strobile crenulate. 



Male genital aperture marginal, about middle of segment. 



Habitat. — Mustelus canis, spiral valve, one specimen. Wood's Holl, 

 Massachusetts, August 11, 1887. 



The only details that the small amount of material at hand permits 

 relate to the disposition of the hooks on the proboscides. The largest 

 hooks are 0.04 mm in their greatest length, and 0.02 mm broad at base. 

 The smaller hooks are from 0.01 to 0.02 mm in length, and from 0.004 mm 

 to 0.01 mm in breadth. The spiral series of hooks -are 0.035 mm apart, 

 and the hooks in each series are situated from 0.01 mm for the larger 

 to 0.02 mm for the smaller from each other. The arrangement seems to 

 be as follows : On the outer side of the proboscis there are four longitu- 

 dinal rows of large, strongly recurved hooks. On the opposite or outer 

 side there are four longitudinal rows of hooks, much like the large 

 hooks in shape and proportion, but having only about half their lineal 

 dimensions. The series of large hooks is flanked on each side by two 

 rows of hooks which are somewhat smaller and proportionally a little 

 more slender than the large hooks. Between each of these two series 

 of intermediate hooks and the inner series of small hooks there is a 

 single row of hooks consisting of alternately large and small hooks. 



