74 CEYLON PEARL OYSTER REPOKT. 



which gives the Cestode a longitudinally striped appearance, darker bands where 

 the glands are present alternating with lighter areas where they are not. 

 Habitat : Intestine of Trygon sephen. 



Prosthecobothrimn trygonis, n. sp. Plate V., figs. 80, 81, 82 ( and b). 



One specimen of this Cestode was taken from the intestine of Trygon walga and 

 three from Trygon sephen. The longest measured when preserved 120 millims. in 

 length. The worm is very slender and soft and anteriorly very narrow, - 5 millim. 

 only in breadth, though posteriorly it broadens out to a couple of millimetres. 



The head is 1 millim. in width. It is square, something like a cushion which is 

 indented in the centre and along the lateral and dorso- ventral axes. The head is 

 thus divided into four squares of equal area, and each of these squares bears at its 

 external angle anteriorly a large hollow or bothridium, on the anterior edge of which 

 lie the hooks mentioned below. Behind each is a single, round, rather small but 

 quite conspicuous sucker. This sucker is a simple sucker and has no sub-divivions or 

 areolas. On its surface each of the four squares bears two hooks more or less connected 

 at their base ; each hook is forked and consists of two unequal-sized prongs ; of these, 

 that which is next the diagonal lines or lines joining the bases of the suckers is the 

 larger and bears a tubercle at its base. The hooks are dark brown, chitinous-looking 

 structures. 



The neck is very long, 2 centims. or 3 centims. at least. It is smooth and 

 traversed by a number of longitudinal muscle bands which are conspicuous through 

 the epidermis. They split up in a symmetrical way in the head. 



The proglottides are extremely numerous, they have salient posterior angles. They 

 always remain somewhat broader than they are long, even at the posterior end. 

 except perhaps the very last. This species obviously differs considerably from that 

 described by van Beneden in his " Becherches sur les Vers Cestoides"'* under the 

 name Acanthobothrium dujardini, especially in the relative proportions of the head ; 

 in our worm this is broader than long, in van Beneden's it is longer than broad. 



The diagnosis of Prosthecobothrium trygonis is : 



Slender Cestode some 12 centims. in length. Head square and divided by depres- 

 sions into four equal squares. Each of these bears a sucker at its free corner and on 

 the surface a pair of unequally two-pronged hooks. Neck very long. Proglottides 

 very numerous, with very salient edges, never longer than broad, except perhaps the 

 last. 



Habitat : Trygon walga, Mull, and Henle, and Trygon sephen (Foesk.), in the 

 spiral intestine. 



Tetrarhynchus leucomelanus, n. sp. Plate V., figs. 83, 83 and 84. 

 This large species of Tetrarhynchus was found in the intestine of Trygon sephen. 



* ' Mem. Ac. Belgique,' xxv., 1850, p. 133. 



