CESTODE AND NEMATODE PARASITES. 77 



one of the four hooked proboscides. The head is 6 millims. long, and swells out a 

 little behind where the muscular sheaths of the proboscides lie. When alive, there is 

 a patch of pink anterior to these sheaths. Each proboscis bears on its concave side 

 when unrolled a number of strongly recurved teeth, which gradually pass into a much 

 straighter, sabre-like tooth on the convex side (Plate V., fig. 876). The recurved 

 teeth have a marked anterior process something like a sword-guard, where the tooth 

 passes into the haft, which is embedded in the tissue. This is absent in the more 

 sabre-like teeth. The teeth are in rings, which are not obliquely placed. 



There is practically no neck, and the number of the proglottides is small, some 

 30 to 35. Until the last three or four, the sides of the proglottides are parallel, 

 straight at their ends, and with no sign of overlapping. The whole body is marked 

 by a curious longitudinal striation, which is due to the presence of minute pigment 

 spots, and to the fact that these little brownish particles are arranged along certain 

 longitudinal lines ; also these pigment spots seem broken up into other areas, which 

 give a mottled appearance to the skin. 



The last four or five proglottides are remarkable for the enormous development of 

 the genital pore, which sometimes occupies one quarter to one third of the length of 

 the proglottis. From this gaping cavity a minute penis protrudes. These same four 

 or five proglottides lose their uniform shape, and become very irregular in outline. 

 The pores are in all cases lateral and irregularly alternate. 



The diagnosis of Tetrarhynchus macroporus is : 



These Cestodes are about 25 millims. in length and 1 millim. in breadth. They 

 have small lappets, turned forward, hooks recurved sabre-like, in straight lines ; no 

 oblique rows. Proglottides number about thirty, and the last four or five are distorted 

 by the enormous development of the genital pore. 



Habitat : The intestine of Trygon uarnak. 



Thysanobothrium, n. gen. 



Length 7 centims. ; posterior proglottides being 1'5 millims. to 2 millims. long. 

 Head squarish, with a sheath bearing four minute suckers at the angles ; within the 

 sheath a rounded knob, and between the sheath and the knob a ring of some twenty 

 finger-like tentacles stretched forward. Neck long. Genital pores very irregularly 

 alternate. 



Thysanobothrium uarnakense, n. sp. Plate V., figs. 88 to 91. 



This remarkable form attains, for a tapeworm parasitic in Elasmobranchs, consider- 

 able proportions. Our largest specimen measured 7 centims., arid in this animal the 

 posterior proglottides reached a length of 1*5 millims. to 2 millims., and a breadth of 

 1 millim. The anterior end of the body is, however, very slender, 0'3 millim. to 

 0'25 millim. in width, but the head, though small, is somewhat wider than this, and 

 attains a breadth of at least 0*5 millim. 



