FURTHEK REPORT ON PARASITES. 51 



the family PnYLLOBOTHRHDyK, and not very far from the genus Phyllvbothrium, 

 VAN BEN. 



Tetragonocephalum trygonis, n. gen. et sp. Plate, figs. 3, 4, 5, G, 7 and 8. 



A number of very minute Cestodes were found in the alimentary canal of Tryyon 

 walga. It frequently happens that most delicate tapeworms are found in the most 

 powerful and voracious Elasmobrauchs, and nothing could be more delicate and fragile 

 than the Cestodes in question. The worms are fragile, and very limp when preserved 

 in formalin. They do not lie stiff and distinct as do those described above from 

 sEtiobatis narinari, but they are entangled together and form a mass like a knot of 

 chewed fine white cotton thread (Plate, fig. 3). 



The head forms a distinct knob, hardly more than visible to the naked eye, 

 borne on the slender neck. Its diameter is some 0'03 millim. and its autero-posterior 

 axis is usually rather less than its diameter from side to side. In some specimens, as 

 in the one shown in fig. 3, the head is swollen, and its longitudinal axis is longer 

 than its transverse. It is a curious cushiony-looking head, consisting of two 

 distinct parts. Anteriorly there is a circular and rounded knob, about twice as broad 

 as it is long and resembling in shape the stones which are used in the Scottish sport 

 of curling. This probably corresponds with the rostellum of other forms. It is 

 quite unarmed (Plate, fig. 4). This rounded rostellum rests on a second region 

 like a crown upon a cushion. This second region is square in outline, and at each 

 of its corners it carries a small but distinct sucker, the orifice of which is minute. 

 From these suckers small papillae protrude, passing through their orifice. The 

 rostellum is separated from the square sucker-bearing portion by a thick basement 

 membrane, and it is traversed by many muscle bundles. Similar bundles are attached 

 to the hinder surface of this basement membrane and run down into the neck, where 

 they soon fade away. 



The neck is short, and the narrow strictures separating the nascent proglottides 

 commence close behind the head. The constrictions between the proglottides always 

 remain slight ; the older proglottides somewhat resemble those of Dipylidium 

 citvumerinum, but are less distinct and, except for the slightest possible thinning 

 between adjacent proglottides, the posterior part of the Cestode, after it has attained 

 a certain dimension, remains the same width throughout. At the same time, every 

 here and there there are constrictions which do not seem to correspond with the 

 divisions between proglottides. These are well shown in Plate, fig. 3. 



The reproductive apertures are lateral, and the penis lies concealed in a spacious 

 recess (Plate, fig. 6). The pores irregularly alternate, some four being in the 

 left followed by one or two on the right, then a few on the left and again perhaps 

 four on the right. At its first appearance the uterus seems double, an anterior and 

 a posterior part lying one in front and one behind the genital pore ; the two are, 

 however, in communication by a narrow channel (Plate, figs. 5, G and 7). The 



H 2 



