AKT. 21. PARASITES OF SHARKS AND SKATES LINTON. 63 



spines, more or less recurved at the tip ; sheathes spiral ; bulbs ellip- 

 tical-oblong, rather short. 



Strobile very slender; segments beginning near the scolex, soon 

 becoming as long as broad, and lengthening rapidly ; last proglottis, 

 immature, length, 2.00 mm., breadth, 0.26. 



Only immature proglottides were seen. These are exceptional in 

 that the cirrus and cirrus-pouch are so poorly developed as to be 

 barely distinguishable, what were interpreted as their rudiments 

 being made out only in the two last proglottides. In a proglottis 

 measuring 2.6 mm. in length, the rudiment of the genital pore was 

 situated at the posterior third, i. e. 0.84 from the posterior end, 

 but a short distance in front of the ovaries. A similar rudiment, 

 similarly placed was seen in another proglottis. In these proglot- 

 tides the testes Avere well developed, and occupied practically all 

 the interior, both in front of the ovary and behind it. The ovary 

 could be distinguished in the two posterior proglottides. It is two 

 lobed, the lobes lying opposite each other on either side of the median 

 line. In a proglottis which measured 2.52 mm. in length, the 

 posterior margin of the ovary was 0.5 mm. from the posterior end of 

 the proglottis. 



Dimensions of specimen in balsam: Length of strobile, 24.5; 

 scolex, length 1.09, length of bothrium 0.34, breadth 0.36, diameter 

 of neck at bulbs 0.32; contractile bulbs, length 0,24, diameter 0.06; 

 length of posterior proglottis 2.60, breadth 0.40 ; diameter of probos- 

 cis, excluding hooks, 0.030, including hooks, 0.054; length of large 

 stout basal hooks 0.024 ; length of longer hooks, middle of proboscis, 

 0.018. 



Galeocerdo arcticus. 



1914, Aug-ust 12: 1, strobile active, length 26 mm., Woods Hole. 



This cestode appears to belong to this species, which was founded 

 in material from the tiger shark, collected at the Dry Tortiigas. 

 Florida. 



(U.S.N.M., Helm. Coll. 7701.) 



RHYNCHOBOTHRIUM HETEROSPINE Linton, 



1890, pp. 839-840, pi. 12, figs. 3-5. 

 1897b, p. 799; pi. 64, figs. 3-8. 



1900, p. 283. 



1901, pp. 425, 436, 443, 482. 



Squalus acanthias. 



1907, August 15: 2; scoleces attached to plerocerci. 



20183— 25— Proe.N.M.yol.64 37 



