AKT. 21. PARASITES OF SHAEKS AND SKATES LINTON. 21 



m front of the middle of the length of the proglottis. The rudiment 

 of the ciiTiis-pouch is at right angles to the margin. Rudiments of 

 the vagina and uterus lie along the median region from the base 

 of the cirrus-pouch is at right angles to the margin. Rudiments of 

 transverse streak on the posterior border of the proglottis, thicken- 

 ing at the median line, the thickening probably representing the 

 rudiment of the shell gland. A broad, granular marginal space 

 represents the vitellaria which appear to form a continuous mass 

 within the muscular layer. The rudiments of the testes are the 

 most conspicuous feature of these immature proglottides. They lie 

 on either side of the median space back of the level of the cirrus- 

 pouch. In front of the cirrus-pouch they are continuous across the 

 median line, and are continuous with lateral masses in the posterior 

 portions of the proglottis, except where interrupted by the cirrus- 

 pouch. 



The average breadth of ten mounted scoleces is 0.65 mm. ; the 

 largest, which is considerably compressed, is 0.98, and the smallest 

 0.46 mm. broad. 



Dimensions of a specimen mounted in balsam : Length 18 ; diam- 

 eter of scolex 0.70 ; bothrium, length 0.35, breadth 0.31 ; breadth 

 of neck 0.35 ; distance to first segment 4.9 ; first segment, length 0.07, 

 breadth 0.32; last segment, length 0.28, breadth 0.43. In another: 

 length about 25 mm., the maximum breadth is 0.72; penultimate 

 segment, length 0.35, breadth 0.56. The last segment tapers to a 

 bluntly rounded point. Diameter of auxiliary sucker, measured on 

 a section, length, 0.075, breadth 0.090. In a strobile which has not 

 been compressed the penultimate segment is 0.46 in length and 0.24 

 in breadth. 



This species has been found in the hammerhead shark {Cestracion 

 zygaeno.) on the following dates: 

 ■ ry/^e.— U.S.N.M., Helm. Coll. 7671. 



1911, July 5: Number not ascertained; associated with large num- 

 bers of other small cestodes in the spiral valve. 



1913, August 18 : 9. 



1915, July 19: A few specimens, collected by Dr. G. A. Mac- 

 Callum. 



Following are extracts from notes made on living material, col- 

 lected July 5, 1911 : This species was easily separted from the other 

 small cestodes found in the spiral valve of a large hammerhead, on 

 account of its stouter habit, and its tendency to throw the body 

 into a close spiral. They also exhibited more vitality than the 

 others. After lying over night in sea water they were still in good 

 condition and active, rather more active than any of the other 

 species. The bothria are cruciformly placed, and are characteristi- 

 cally thick and muscular. There is an acetabulum, and the border 



