CESTODE AND NEMATODE PARASITES. 69 



on the body of the species. Two individuals were dissected ; in one the remains of a 

 number offish, including a young Pristis sp., were found, in the other only crustacean 

 fragments. The parasites were few in number and all belonged to one species of 

 Tetrarhynchus. 



The largest specimen of this Tetrarhynchus attained a length of 5 centims. but 

 since some loose proglottides measured 4 millims. each, probably the full length is 

 greater and its posterior end a width of 1 millim. The length of the head is 

 4 millims. The lappets are short and widely separated ; anteriorly they occupy 

 1 millim., and the remaining 4 millims. are equally divided between the part of the 

 head which contains the proboscis tubes and the part which contains the proboscis 

 bulbs. The part of the head which bears the lappets is 1'2 millims. broad, but 

 behind this the head tapers. The colour of the living specimens is an opaque 

 milk-white. 



The hooks in the proboscides are arranged in longitudinal rows and also in rings ; 

 the latter are. almost horizontal, there being only a very slight trace of obliquity as 

 they surround the stem. One peculiarity which we have not noticed in other species 

 is that on each proboscis there is a longitudinal row of hooks, whose points are reversed 

 and look towards the tip of the proboscis and not to the base, as do all the others. 

 The shape of the hooks is shown in fig. 7 1 ; some of them are not nearly so hooked as 

 others and pass into sabre-like forms. 



Another peculiarity is that the outer muscles of the proboscis bulb are very oblique, 

 very clear, and cross one another at right angles, giving a " Malvolio, cross -gartered" 

 appearance to these structures. 



There is a short neck, and then a number of proglottides, five or six times as 

 broad as long, separated one from another by perfectly straight lines and with at first 

 parallel straight sides. They soon, however, begin to lengthen, and at the end of the 

 first quarter they are square. The sides also begin to bow outwards, but the ends 

 are always flat, and there is absolutely no overlapping. 



The reproductive pores are lateral and at the juncture of the anterior two- thirds 

 with the posterior third. Their circular lips are prominent and everted. The pores are 

 irregularly alternate ; for instance, starting at the last of one specimen, they run as 

 follows : 1 right, 3 left, 2 right, 1 left, 1 right, 2 left, and so on. 



The diagnosis of Tetrarhynchus rhynchobatidis is : 



Five centims. long, posteriorly 1 millim. broad. Head with small lappets. Milk- 

 white when alive. Proboscides with longitudinal rows of hooks, one row being 

 turned the wrong way, hooks also arranged in nearly horizontal rings. Proboscis 

 bulb chequered by external, obliquely-placed muscles, crossing each other at right 

 angles. Proglottides not overlapping. Genital pores with everted lips, lateral, 

 irregularly alternate, situated at anterior border of last third of the proglottis. 



Habitat : Intestine of Rhynchobatus djeddensis. 



In another specimen of Rhynchobatus djeddensis were a couple of single proglottides 



