Helminth Fauna of the Dry Tortugas. 183 



The species has some suggestion of R. lomentaceum. 



Dimensions, in millimeters, of specimen mounted in balsam : Length 

 3.5 ; head, flattened, breadth 0.56; length of bothria 0.40; bulbs, length 0.72, 

 breadth 0.12; diameter of neck, flattened, anterior 0.38, posterior 0.56: 

 proboscis, length (estimated) 3, diameter, exclusive of hooks, base 0.05, 

 near apex 0.04; hooks (at base shorter and more crowded than at apex), 

 length, at base 0.014, near apex 0.028. 



From spiral valve of nurse-shark (Ginyliinostoma cirratum). July 

 5, one. 



25. Rhynchobothrium sp. 



(Plate 10, figs. 70-74.) 



Bothria foliaceous, but with margins somewhat thickened ; head much 

 broader than neck ; neck slender, cylindrical, enlarging at bulbs ; sheaths in 

 close spirals ; bulbs long-oval, with retractor muscle attached at about the 

 middle of the length on the median wall ; proboscides long, hooks of differ- 

 ent sizes and shapes. The most marked differences are to be seen in those 

 hooks which are near the base of the proboscides. On one side there are 

 some small, straightish spines ; on the other they are much larger ; long and 

 nearly straight, but with an abrupt curve at the apex. A single row of these 

 large hooks extends around to the opposite side a short distance from the 

 base. The proboscides were not seen fully extended. So far as seen, the 

 hooks on one side remain small, slender and very sharp-pointed, but grow 

 larger toward the apex, so that in the completely everted proboscis the dif- 

 ference between the hooks of the opposite sides is probably slight. The 

 large hooks with abruptly recurved ends are confined to the basal region. 

 Beyond the base the larger hooks become rather broad, in lateral view, and 

 are strongly and uniformly curved. On the other hand, among the small 

 hooks some distance from the base are hooks which are straightish with 

 abruptly curved tips. Towards the tip of the proboscis, as may be seen 

 in the retracted part, a prevailing form is a slender hook curved m two 

 directions, like a letter S nearly straightened out. 



Transverse striae begin immediately below the neck. The first distinct 

 segments are shorter than broad, but soon become as long as broad. They 

 then rapidly and uniformly lengthen, but remain about the same breadth. 

 The posterior segments are nearly ten times as long as broad, and their 

 anterior ends are abruptly larger than the posterior end of the preceding 

 segment. None of the segments were mature, although rudiments of repro- 

 ductive organs could be made out. In the next to the last segment the 

 rudiment of the cirrus bulb was a little behind the posterior third, and the 

 ovary was at the posterior fifth. The anatomy of the posterior segments. 

 so far as it could be made out, is much like that of R. exile. 



Dimensions, in millimeters, of specimen mounted in balsam: Length 15; 

 length of head and neck 2.4 ; breadth of head 0.73 ; bothrium, length 0.48, 



