JLRT. 21. PARASITES OP SHARKS AND SKATES LINTON. 83 



RHYNCHOBOTHRIUM TENUISPINE Linton. 



1890, pp. 837-838, pi. 12, figs. 1, 2. 



18970, pp. 448-449, pi. 84, fig. 8. 



1905, p. 348 (adult), p. 395 (larva), fig. 101. 



19100, p. 695. 



1911, p. 588. 



Adult stage. 



Dasyhath centrura. 



Collected in 6 of the years from 1903 to 1920: On 2 dates in 

 August, many on one date, 1, length 4 mm. on the other; on 4 dates 

 in September, 1 to very numerous. There was a conspicuous red 

 blotch in the neck, in specimens collected on one of these dates, 

 which, in some cases involved the bulbs, and was easily visible to the 

 unaided eye, ova with bristles. On one date in October, 1, length 

 15 mm., length of posterior segment 4 mm., number of segments 7, 



1923, July 7, many; August 15, 20; August 20, 5. 



This species is characterized b}' the relatively long proboscides, 

 which are thickly beset with minute, spinose hooks. 



(U.S.N.M., Helm. Coll. 7711.) 



Raja einnacea. 



1906, August 27 : 1, scolex with plerocercus attached. 



RHYNCHOBOTHRIUM, species. 



A RhynchohothHwm (figs. 91-94) which is near R. tenuispine, but 

 differing from typical representatives of that species in the rela- 

 tively coarser and more sparsely set spines is recorded here for the 

 present. 



This form was found on two occasions, September 22, 1906, and 

 September 1, 1920, one specimen on each date, and associated with 

 typical representatives of R. tenuispine. 



The bothria are rather widely separated; proboscides long and 

 slender; hooks small, of about uniform size, somewhat sparsely set, 

 except at the base of the proboscis, where they are close set on a 

 slight enlargement, as in R. tenuispine. Strobile slender, immature ; 

 proglottides begin near the scolex, and increase in length rapidly. 

 There were about nine segments in all, the last one making up nearly 

 half the length of the strobile back of the scolex. Dimensions of 

 specimen in balsam: Length 5; length of scolex, 1.06, of bothrium 

 ■0.29; breadth of bothrium 0.35; diameter of scolex at contractile 

 bulbs 0.22 ; length of bulbs 0.43, diameter 0.07 ; diameter of proboscis, 

 excluding hooks, 0.015, including hjoks 0.021 ; length of hooks 0.006 ; 

 length of last segment 1.91, breadth 0.21. 



Again on July 7, 1923, 1 similar form was found among many 

 typical R. temdspine. In some particulars these forms suggest R. 

 hispidum. 



