86 CEYLON PEARL OYSTER REPORT. 



Diagnosis of Tetrarhynchus macroc&phalus : 



The characteristic features of this species are the relatively enormous head, the few 

 some teu or twelve proglottides, the " herring-bone " spicules on the proboscides, 

 and the arrangement and grading of the hooks on the same. 



Habitat : The stomach and intestine of Trygon walga. 



Tetrarhynchus platycephalus, n. sp. Plate VI., figs. 113 and 114. 



This is a moderate-sized form, measuring 10 millims. or 12 millims. in length. The 

 head and neck occupy about one-sixth of the whole body length. The head is 

 compressed from front to back and spreads out laterally, having something the 

 appearance of a Toreador's hat. The four-hooked proboscides bend out towards the 

 edge of the hat, and finally emerge at the angles (Plate VI., fig. 114). The hooks are 

 large, sabre-like, and of uniform size. 



The body consists of ten or eleven segments, the last two of which are as big as the 

 rest of the body altogether. The proglottides are at first some six times as broad as 

 they are long, but the fourth or fifth proglottis is already square, and the last is 

 perhaps four or five times as long as broad. They are rounded and plump, stouter 

 half way along than at either end, and stouter in front than behind. The most 

 characteristic feature is the genital pore. This is a great cleft which runs almost 

 half across the proglottis and seems to half cut it in two. This appears already in 

 the fourth or fifth proglottis, and gives the appearance of an irregular and abnormal 

 segmentation. The pores are lateral and alternate as a rule, though now and then 

 two will consecutively follow each other on the same side. 



The diagnosis of Tetrarhynchus platycephalus is as follows : 



Head much flattened, proboscides coming out of the edges of the flattened head. 

 Hooks uniform in size, sabre-like. Proglottides ten or eleven in number, broader in 

 the middle than at either end. Reproductive pore resembles a huge cleft, which seems 

 to half cut the proglottis in two ; alternate, but slightly irregular. 



Habitat : The intestine of Trygon walga. 



Tetrarhynchus rubromaculatus (Diesing). Plate VI., figs. 115 and 115a. 



This is by far the smallest of the Tetrarhynchids found in Trygon walga. Only 

 two specimens were taken, one measuring 4 millims., the other 7 millims. in length. 

 The head occupies nearly half this length, and the proboscis sheaths, which vary a 

 little in the two specimens, are nearly half the length of the head (Plate VI., fig. 115). 



The bothridia are distinct even when the proboscides are protracted. The latter 

 are four in number and bear sickle-shaped spines, not arranged in very definite 

 rows ; between some of them are short rows of minute straight spines. 



Behind the head the body consists of six or seven proglottides: the first two of 

 these are band-like, the third longer, the fourth about square, the fifth twice as long 

 as broad, the sixth and seventh four to five times as long as broad. In one specimen 



