840 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [122] 



narrow notch. Since these varieties graduate into each other, it can be 

 readily understood that there must be much diversity in the shape of 

 the hooks of this species. Some of the straight, slender hooks, when 

 seen as they lie on the side of the proboscis which is directly iu view, are 

 quite broad toward the base, being flattened in a plane which is at right 

 angles to the longitudinal axis of the proboscis. These hooks when 

 seen in this position with their broad basal supports look like broad, 

 thin tacks. Eight or nine hooks can be seen at once in a single trans- 

 verse spiral. The longest hooks that were measured were near the base 

 of the proboscis. The hooks vary in length from 0.013 to 0.027 mm . The 

 average length is perhaps not far from 0.016 mm . 



33. Rhynchobothrium imparispine, sp. nov. 

 [Plate xii, Figs. 7-9.] 



Bothria two, lateral, oblong-elliptical, distinctly emarginate poster- 

 iorly, deeply hollowed out on the face, margins slightly inverted, very 

 versatile, head quite broad, bluntly sagittate, the bothria flaring out- 

 ward at their posterior edges, approaching each other but not touching 

 anteriorly. Neck three or four times as long as the head, cylindrical in 

 front, flattened posteriorly. Proboscides long, moderately slender, 

 armed with hooks which present great differences both in shape and 

 size; sheaths spiral ; contractile bulbs long, slender, tapering slightly 

 posteriorly. First segments begin a short distance behind the neck, 

 exceedingly short, subsequently increasing in length uniformly, becom- 

 ing at length elliptical-oblong and longitudinally striated. Ultimate 

 and free segments much longer than broad, with about fourteen longi- 

 tudinal muscular stria? on a lateral side. 



Genital apertures ; male, marginal near posterior end, from deep 

 rectangular marginal notch. Length 50 ,,l,n . 



Habitat. — Baia erinacea, spiral valve, one specimen, Wood's Holl, 

 Massachusetts, August 29, 1887. 



On August 29, 1887, I examined twenty-four specimens of the Sum- 

 mer-skate (Rata erinacea). Their stomachs were filled with small Crus- 

 tacea, mostly shrimps (Grangon vulgaris), and annelids of the genera 

 Nereis and Rhynchobolus. The entozoa from this lot of skates were 

 several specimens of Echeneibothrium variabile from the spiral valve of 

 some, a number of Nematods from the stomach and spiral valve of some, 

 and a single Rhynchobothrium, the subject of this sketch. 



The living specimen was very active when placed in sea-water and 

 changed its form so incessantly that it was impossible to obtain satis- 

 factory measurements. The bothria were plainly two, although appear- 

 ing bilobed, on account of the deep posterior emargination. They were 

 very versatile and were frequently directed forward, assuming then a 

 cupular shape. The last segments were plump, the whole worm being 

 in fact rather thick. The length was 50 mm ; breadth of head, l nnn ; 



