"101] NOTES ON ENTOZOA OF MARINE FISHES. 819 



rf the distortion resulting from compression. Behind the hooks the 

 }othria contain a great many circular fibers, which are arranged con- 

 centrically, with the hooks as a center. Some of these concentric fibers 

 ire attached to the base of the hooks. Other fibers, also attached to 

 Dhe base of the hooks, cross the circular fibers radially and extend back 

 through the bothria parallel with their long axis. Both of these sorts 

 }f fibers are exceedingly delicate. The circular muscles evidently effect 



e motion of circurnd notion or rotation in the hooks, while the radial 

 iiuscles effect the motions of abduction and adduction respectively. 

 Short, blunt processes on the under side of the hooks afford means of 

 ittachmeut for the muscles. These processes are on the under side of 

 :he inner prongs of the hooks. In this compressed, stained specimen 



e pads or cushions, \vhich bear the supplemental disks, are emargin- 

 ite posteriorly and have therefore a cordate shape. The supplemental 

 lisk measures .07 11 " 11 and .06 mm in its two diameters, inside measurement. 

 Che largest bands of muscular fibers in the neck are .04S IU1U broad, a 

 single fiber measuring as much as .004 mm in breadth. The bundles of 

 ibers in the neck can be seen plainly in specimens which have not been 

 3ompressed. They are usually sinuous or waving in outline. 



The smaller specimens have many characters in common with Van 

 Beuedeu's Acanthobothrium ditjardinii (Prosthccobothrium dujardinii 

 Dies.), but as Van Beneden describes and figures that species as having 

 the bothria destitute of transverse costre, and, moreover, each provided 

 with a posterior versatile flap, there can not be even a generic identity 

 stablished between the two species. If Van Beneden's species had 

 jeeu based on alcoholic specimens one might suppose that he had mis- 

 taken the posterior fossette for a posterior appendage ; I have "seen 

 such a deceptive appearance as this in a few alcoholic specimens. This 

 consideration is hardly admissible, however, as Van Beneden mentions 

 ;he extraordinary versatility of this posterior flap in active worms. 



A. paiilum differs from A. coronatum principally in its very much 

 smaller size and in the different proportions of its segments. 



PHOREIOBOTHRITJM Liuton. 



24. Phoreiobothrium lasium Lt. 



Report of IT. S. Fish CommissioLer, pp. 474-476, Plate iv, Figs. 24-29. 



I encountered this parasite twice in the summer of 1887 at Wood's 

 Holl, Massachusetts, each time in the dusky shark (Carcharias obscurus). 

 The first lot, collected July 25, contained nine specimens, two of them 

 small ; the second lot, collected August 12, contained fourteen speci- 

 mens. Since the description which I have given for this species was 

 based on alcoholic specimens, I add the following data obtained from 

 living specimens : 



One specimen had the following dimensions while living: Length, 

 32mm . i^gt^ o f bothria, .48 mm ; breadth, .26 min ; length of hooks, longest 



