820 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [102] 



prong, .14 mm ; diameter of head in front, ,48 mni ; at posterior end, .62 mm j 

 diameter of nock, .13 mm ; distance to first segment, .8 mm ; length of seg- 

 ment, 10 nim from head, .lG mm ; breadth, .lG mm ; length of last segment, 

 1.2S lnm ; breadth, ,42 m,n ; number of distinct segments, sixty. The spec- 

 imen was slightly flattened under the compressor. 



Another specimen of the same lot was 35 mm in length ; its last seg- 

 ment 1.12 mm in length and .5 m,u in breadth. 



The proportions of the living worm do not differ materially from those 

 of alcoholic specimens. It was observed, however, that after they had 

 lain for twenty- four hours in sea water the specimens were not so 

 straight nor symmetrical as at first. The apparent varieties in pre- 

 served specimens are evidently due to different degrees of contraction. 

 The minute epidermal spines were found in isolated patches on several 

 of the specimens. 



Platybothrium, gen. nov. 



[izXaTTpi, broad.] 



Body articulate, tseniaeforin. Head decidedly flattened, squarish, or 

 trapezohedral. Bothria four, subtriangular, sessile arranged in mar- 

 ginal pairs, armed with compound hooks, and each terminating poste- 

 riorly in a cup-like depression or loculus. A* single indistinct circular 

 depression (supplemental disk ?) on each bothrium in front of hooks. 

 Genital apertures marginal. 



A single specimen furnishing, as I suppose, the type of a new genus, 

 with some characters which ally it to Prosthecobothrium Dies., from the 

 spiral valve of the dusky shark (Carcharias obscurus), presents such 

 decided differences from any genus included in Diesing's Revisions that 

 I am obliged, for the present, to describe it under a new generic name. 

 In the flattened head and marginal pairs of bothria it is unique among 

 the armed Phyllacanthince. An objection to referring the specimen to 

 the geuus Prosthecobothrium is that the apparent homologue of the pos- 

 terior bothrial appendage which is characteristic of that genus is, in 

 this specimen, to be regarded rather as a loculus formed by a transverse 

 costa near the posterior end of the bothrium, or as a kind of posterior 

 cupping disk. Further, there is a faint indication of a single supple- 

 mental disk on each bothrium in front of the compound hooks. 



Again, the doubtful character of the supplemental disk, tha single or 

 no transverse costa, and the character of the hooks exclude the genera 

 Calliobothrium, Acanthobothrium, and Onchobothrium. The flattened 

 bothria and their arrangement in marginal pairs exclude the problemat- 

 ical genus Cylindrophorus as well as Phoreiobothrium. 



25. Platybothrium cervinum, sp. nov. 



[Plate viii, Figs. 8-10, and Plate ix, Fig. 1.] 



Head quite flat, squarish, rhomboidal or irregularly hexagonal in 

 outline, in lateral view j thickness less than half the breadth. Bothria 



