CESTODE AND NEMATODE PARASITES. 83 



exceeded 150 millims. The width gradually increased as we passed backwards until 

 the last half dozen proglottides, which narrowed a little (Plate VI., fig. 104). When 

 alive the worm was in all probability much longer ; they contract when being killed. 



The head resembles the figs. 2 and 3 of VAN BENEDEN'S pi. iv. of his " Recherches 

 sur les vers cestoiides,"* which represent Phyllobothrium lactuca, but the bothria 

 are more definitely arranged in four, and the edge, which is crinkled and ruched, 

 has not such a square section (Plate VI., fig. 105). The neck is very long. 

 The proglottides all through the body are broader than they are long, except the 

 posterior six or seven, which are slightly longer than they are broad. Each 

 proglottis overhangs the ones which follow it, and thus its posterior border is wider 

 than its anterior. The sides are oblique and, as the figures show, slightly wrinkled. 



Habitat : Intestine of Trygon walga. 



Tylocephalum trygonis (SHIPLEY and HORNELL). 

 Tetragonocephalum trygonis, SHIPLEY and HORNELL. 



Several specimens of this species were found in the intestine of Trygon walga. 

 They permitted one to observe what was not recorded in the original description,! 

 that the genital pores are very irregularly alternate. Thus in one specimen, using 

 R, for right and L for left, the genital pores were arranged as follows : R 6, L 2, 

 R 1, L 2, R 1, L 1, K 1, L 1, R 3, L 1, R 2, L 2, R 3, L 2, and so on. In the 

 posterior segments the pore is very large and stands out from the proglottis just as 

 the portion which bears the leaf stands out from a bare twig of a chestnut tree in 

 winter. 



Tetrarhynchus equidentatus, n. sp. Plate VI., figs. 106 and 107. 



This is, I think, the largest Tetrarhynchus I have seen, and it is certainly very large 

 to come from the alimentary canal of an Elasmobranch. Unfortunately but one 

 specimen was taken, and this measured 47 centims. in length, not a very great 

 length ; but it is the breadth which gives the magnitude to this animal. It is almost 

 uniformly 3 millims. broad from one end to the other, though it increases very slightly 

 as we pass backward, but the last proglottis is narrowed. It is perhaps 0'3 millim. 

 thick. 



Compared with the size of the body, the head is very small, and the muscular 

 sheaths come right up to the anterior end of it, and thus there are no more or less coiled 

 tubes between them and the base of the exserted proboscides. The proboscides bear 

 spiral or rather obliquely placed rings of hooks ; the hooks are all of precisely equal 

 size and most regularly arranged. They are 0*049 millim. in length. The head bears 

 laterally well-marked lappets or bothridia. It is succeeded by an unsegmented region 



* ' Mem. Ac. Eelgique,' xxv., 1850. 

 t This Eeport, Part III., p. 51. 

 M 2 



