[101] NOTES ON ENTOZOA OF MARINE FISHES. 819 



of the distortion resulting from compression. Behind the hooks the 

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

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

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

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

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

 of fibers are exceedingly delicate. The circular muscles evidently effect 

 the motion of circumduction or rotation in the hooks, while the radial 

 muscles effect the motions of abduction and adduction respectively. 

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

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

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

 the pads or cushions, which bear the supplemental disks, are emargin- 

 ate posteriorly aud have therefore a cordate shape. The supplemental 

 disk measures .07 mm and .06 ,um in its two diameters, inside measurement. 

 The largest bauds of muscular fibers in the neck are .048 ,nm broad, a 

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

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

 compressed. They are usually sinuous or waving in outline. 



The smaller specimens have many characters in common with Van 

 Beneden's Acanthobothrium dujardinii (Prosthecobothrium dujardinii 

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

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

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

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

 been 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 

 the extraordinary versatility of this posterior flap in active worms. 



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

 smaller size and in the different proportions of its segments. 



Phoreiobothrium Linton. 



24. Phoreiobothrium lasium Lt. 



Report of U. S. Fish Conimissiouer, 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 (Garcharias 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, 

 32 mm ; length of bothria, .48 mm ; breadth, .26 mra j length of hooks, longest 



