48 CEYLON PEARL OYSTER REPORT. 



form a new genus which we have called Myzophyllobothrium. This form obviously 

 comes near Phyttobothrium, but there is no neck and there is a distinct " myzo- 

 rhynchus." It is a much larger form than Hornellobothrium cobraformis found in the 

 same specimen. 



The worm is a long one for a Selachian parasite, measuring some 8 centims. in our 

 longest specimen, and about 0'4 millim. broad. The head is 1 millim. across. It 

 consists of a terminal myzorhynchus which bears four almost terminal suckers ; the 

 whole is very delicate, transparent, mobile and capable when alive of great extension. 

 The myzorhynchus is flanked by four bothria or sessile, leaf-like extensions ; these also 

 bear at their apex a small thickening which may represent a sucker. The edges are 

 not crumpled and wrinkled as in Ph. lactuca, but are smooth and entire. 



There is practically no neck. The proglottides are cut off from one another by 

 perfectly flat partitions at right angles to the surface. The two sides of each 

 proglottis in the anterior half of the body are flat and, as nearly as possible, 

 parallel ; behind this the sides become somewhat bowed outward, and thus there is 

 a constriction at the "joint." There is no trace of overlapping of the posterior end 

 of a proglottis over the anterior end of the next succeeding. The centre of the body 

 consists of proglottides, which are about square ; the most posterior proglottides may 

 reach a length of three times the breadth. 



The testes appear early, and are always accompanied by an L-shaped structure 

 (Plate I., fig. 17a), which has a limb passing from the genital aperture to the centre 

 of the proglottis and then another limb running straight back ; this probably repre- 

 sents the vas deferens and vagina. The posterior proglottides nearly always have 

 their penes protruding. 



When alive, the posterior proglottides readily detached themselves from the worm, 

 and then showed very active movements, crawling about rapidly. 



There is a deposit of granular red pigment just behind the head which seems to 

 accompany the excretory canals ; at any rate, it runs back along the main longitudinal 

 ducts. It contrasts strongly with the general milk-white colour of the worm. 



Habitat : In the spiral intestine of Aetobatis narinari, the individual A from 

 Puttalam Lake. 



Tylocephalum trygonis (Shipley and Hornell). '"' 



Tetragonocephalum trygonis, Shivl. and Horn. 



This species, which has hitherto been recorded only from the intestine of Trygon 

 walga, was found associated with Tetragonocephalum aetobatidis and with Myzo- 

 cephalus narinari in the intestine of Aetobatis narinari. 



* This Report, Part III., p. 51. Since writing this article we have come to the conclusion that the 

 genus we described as TetraguTWcephalwm is identical with Linton's Tylocephalum, 'U.S. Commission of Fish 

 and Fisheries,' Commissioner's Report for 1887, Part xv., 1891, p. 805. 



