ART. 21. PARASITES OF SHAEKS AND SKATES LINTON. 37 



Strobile. — The spines on the neck are longer and larger than in 

 either of the foregoing species. The necks in most of my specimens 

 are very slender. This species shows more irregularities due to 

 different contraction conditions than is the case in either of the 

 preceding species. Adult proglottides are from two to two and a 

 half times as long as broad, with the ends more or less rounded or 

 tapering. The general plan of the anatomy agrees with that of 

 P. lashmi. 



Length of strobile 20.00 30.00 28.00 IL 00 



Breadth of scolex, excluding books 0. 20 0. 16 0. 14 0. 15 



Length of scolex, approximate 0. 12 0. 16 0. 14 0. 15 



Length of hooks, maximum 0.06 0.054 0.054 0.054 



Length of spines on neck, maximum 0. 03 0. 03 0. 03 0. 03 



Distance to first distinct segment 5. 60 3. 90 3. 20 2. 57 



Length of posterior segments 1. 82 1. 92 1. 68 0. 77 



Breadth of posterior segments 0. 70 0. 71 0. 63 0. 44 



Type.— U.S.N.M., Helm. Coll. 768T. 



From spiral valve of Gestracion zygaena. 



1914, August 6 : Few. August 7 : 32. 



The spiral valves from which these cestodes were obtained were 

 given me by Dr. H. B. Goodrich. The sharks from which they came 

 measured 135 and 150 centimeters, respectively. The worms were 

 rather firmly attached to the mucous membrane near the anterior 

 €nd of the spiral valve. The following measurements were- made 

 of living specimens : 



Length of strobiles 24.00 29.00 



Breadth of scolex, slightly compressed 0. 27 0. 27 



Length of bothrium 0. 15 0. 15 



Breadth of bothrium 0.18 0.18 



Length of spines on neck, maximum 0. 35 0. 035 



The scolex is so short that it usually presents nearly a front view 

 when placed under the cover-glass. The neck is long and slender 

 and the whole worm more or less spinose. Spines evanescent, many 

 of them becoming detached when the cover-glass was placed on the 

 worm in sea water. 



PHOREIOBOTHRIUM EXCEPTUM, new species. 



Plate 4, figs. 41-44. 



Scolex. — Bothria enlarging toward the posterior end, which bears 

 six loculi. The hooks appear to be two pronged. These prongs 

 spring from a conical, roughened base which is inclined at an angle 

 of about 45 degrees with the axis of the scolex. The inner tips of 

 the bases of a pair of hooks meet on the median line of a bothrium 

 in the same manner as do the horizontal bars of the three-pronged 

 hooks of the three preceding species. The basal support of the hook 



