806 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [88] 



The character of the head suggests a possible close relationship with 

 Biscocephalum. The large, globular myzorhyuchus of Tylocephalum 

 may be homologous with the broad, muscular head of Biscocephalum, 

 in which case the globular acetabular disk of the former would be ho- 

 mologous with the corrugated, inflated, cervical mass of the latter. If 

 the acetabular disk of Tylocephalum were, in the adult, to divide into 

 independent bothria, it would then exhibit a close resemblance to Van 

 Beneden's IHscobothrium. 



Until more material is obtained the exact position of this Cestod must 

 remain in some doubt. 



20. Tylocephalum pingue, sp. nov. 



[Pinguis, plump.] 



[Plate ix, Figs. 5-9.] 



Head divided into two spherical parts by a median transverse constric- 

 tion, the anterior part a myzorhyuchus, the posterior a bothrial disk, 

 bearing four supplemental disks not evident in the living worm, but 

 when the specimen is made transparent they are seen to be arranged in 

 pairs, which are marginal with respect to the head, lateral with respect 

 to the body. 



Anterior segments begin some distance back of head, very short, 

 much broader than long, subsequently squarish, ultimately longer thau 

 broad. Habit of body rather plump in subcylindrical. Genital aper- 

 tures marginal (?). Length of immature specimen 20 mm . 



Habitat. — Bhinoptera quadriloba, spiral valve, one specimen, Wood's 

 Holl, Massachusetts, July 20, 1887. 



The description of this genus and species is based on the examina- 

 tion of a single specimen. While no sexually mature segments exist 

 the adult or strobile condition is well assured. I shall first give the 

 description made of it while it was yet living, and then add the few 

 observations I have been able to make after a study of the alcoholic 

 specimens. 



When the specimen was first found it was firmly attached to the 

 mucous membrane about the middle of the spiral valve of its host. 

 The anterior part of the head, or myzorhynchus, was imbedded in the 

 mucous membrane. It was carefully removed without damage and the 

 specimen placed in sea water. It then measured 20 mm . Its form was 

 subcylindrical, aud it had an arcuate outline on account of a flexure 

 towards one of its margins. No movements were observed in it at first, 

 and until it was examined with a lens it was taken to be a specimen of 

 some Echinorhynchus. 



The shape of the head was very peculiar, and totally unlike that of 

 any cestod I had ever seen. In my notes made at the time I described 

 it as shaped like a dumb-bell with a very short handle, the axis of the 

 handle coinciding with the axis of the body. The anterior globular 



