16 PKOCEEDINGS OF THE NATIONAX. MUSEUM. vol. 64. 



The material which I have does not warrant an attempt at the 

 revision of these difficult forms. The foregoing observations are 

 made in the hope that they may prove of assistance to future 

 workers. 



MONORYGMA PERFECTUM (van Beneden). 



Plates 2 and 3, figs. 18-31. 



AnthobotJirium perfectum P. J. van Beneden, Mem. sur Les Vers Intes- 

 tinaux, p. 125, pi. 17, figs. 11-14. 



Diesing ^ made the new generic name Monohothrium for this spe- 

 cies. See Zschokke.* 



For more complete bibliography, see Stiles and Hassall.'* 



The material here reported was obtained from the stomach of a 

 sleeper shark {Somniosus brevipinna), Moser Bay, Alaska, June 

 3, 1903, and was sent to me by Dr. C. W. Stiles. 



(U.S.N.M., Helm. Coll. 7669.) 



There are three strobiles in the lot, measuring 55, 70, and 85 mm. 

 in length, respectively. No free proglottides were present, but there 

 were a few short chains of ripe segments. Following are measure- 

 ments of the largest specimen: Length 85; breadth of scolex 3.50; 

 length of bothrium 2.50; breadth of strobile behind scolex 2.50; 

 length of segments 10 mm. back of scolex 0.07, breadth 3; 25 mm. 

 back of scolex, length 0.21, breadth 3.50; 40 mm. back of scolex, 

 length 0.28, breadth 5; 60 mm. back of scolex, length 0.56, breadth 

 5 ; average length of last 15 segments 0.86 ; breadth 4.50. 



Five ripe proglottides, each with the uterus swollen with ova, and 

 bulging out on the ventral side, were 4.75 in breadth, and of about 

 uniform length, 1.6. The thickness through the projecting uterus 

 hump was 2. When pricked, one of these proglottides liberated large 

 numbers of fusiform ova, 0.09 by 0.03 in the two principal diameters. 



Scolex. — As seen in alcoholic specimens the scolex is pyramidal, 

 truncate in front. The bothria are pyriform, the posterior loculus 

 deeply cup-shape, with rather thin, sharply defined borders. The 

 anterior loculus (auxiliary acetabulum) is shallower, almost saucer 

 shape. Transverse sections of the scolex show a central dense mass 

 of deeply staining cells, marking the anterior termination of the axis 

 of the scolex. This appears in five sections of the series, and repre- 

 sents a structure which is a little more than one-third the length of 

 the anterior loculus of a bothrium, and is doubtless to be interpreted 

 as the rudiment of a myzorhynchus (fig. 21) . 



s Sitz. d. kais. Akad. d. Wissens., Wien, vol. 13, p. 583. 



* Recherch. sur la Structure Anatomique et Histologique des Cestodes, pp. 281-294', pi. 

 7, figs. 114-120. 



5 Bulletin 85, Hygienic Laboratory, p. 276. 



