CESTODE AND NEMATODE PARASITES. 51 



broad, and the head is 3 millims, at least in width. T. gangeticus has a smooth, 

 white head, two very clearly denned and large lappets, somewhat heart-shaped, the 

 apex pointing forward and the four proboscides issuing near the two apices, two on 

 each side (Plate II., fig. 28). The proboscides are stout and bear teeth of many 

 sizes. On the concave side of the extruded proboscis are large, strongly recurved 

 teeth ; these are flanked by teeth of lesser size, and they gradually diminish until 

 upon the convex side there are a multitude of fine toothlets. Although it is rather 

 masked, these teeth are really arranged in very obliquely placed rings. 



The edges of the lappets are outstanding and sharply separated from the head, and 

 they have clear-cut edges. 



The proboscis-tubes leading to the proboscis-bulbs are not spirally twisted so much 

 as bent in and out. The head narrows posteriorly, anteriorly it is 2 millims. in width, 

 and the whole is 3 millims. in length. 



There is no neck, the proglottides appear immediately after the head. As there 

 were but three specimens, one only was mounted, and this, which is drawn on Plate II. , 

 fig. 28, shows only just the anterior five or so proglottides. 



The diagnosis of Tetrarhynchus gangeticus is as follows : 



Short (10 millims.), stout (2 millims., and head 3 millims. in breadth) forms. Head 

 with two very clearly cut lappets standing out from general surface. Proboseides 

 stout, with large hooks on one side, diminishing regularly to small hooks on the other. 

 Hooks arranged in oblique rings. Proboscis-tubes bent in and out. 



Habitat : Small intestine of Carcharias gangeticus. 



Tetrarhynchus periderseus, n. sp. Plate II., figs. 29, 30, 30a, 3la, b, c. 



This species was present in large numbers in the small intestine of Carcharias 

 gangeticus. The head, and a peculiar extension of the head in this species, is a well- 

 marked shade of dark grey, which contrasts vividly with the matt-white of the rest 

 of the body. Even in the stained and mounted specimens, peculiar coloured granules 

 can be recognized, which doubtless give rise to this colour in the live animals. 



This is a big species, some specimens attaining a length of 70 millims., possibly 

 more, as the bottle in which they travelled was full of fragments. The width varies, 

 but is never great, and even the head never exceeds about 1*3 millims. The head 

 bears two lappets, but they are so divided in the centre as* to appear like four. They 

 are very compressed into the head and do not stand out. They appear rather 

 puckered at their edges. The proboscides are slender, and bear oblique rows of very 

 minute teeth, all of uniform size (Plate II., fig. 30a). The proboscis-tubes and 

 proboscis-sheath are alike short. The head is produced backwards into a very 

 characteristic collar which overhangs and embraces the anterior part of the body. 

 This is a very marked feature (Plate II., fig. 30). 



There is a fairly long neck, the first trace of segmentation occurring some way 

 behind the posterior limit of the collar. The proglottides have straight sides, and 



H 2 



