CESTObE ANt) NEMATObE PARASITES. 59 



Rhoptrobothrium myliobatidis, n. sp Plate III., fig. 48. 



Of this minute Cestode, one only was available, and that included little more than 

 the head, and was in a poor state of preservation, showing very little histological 

 detail. The length of the worm, which was obviously imperfect, was 1*8 millims.. 

 and the arms of the head when stretched measured 1 millim. from tip to tip. 



The head somewhat resembles the head of Anthobothrium or Echeneibothrium, that 

 is to say there are four arm-like bothridia, but in Rhoptrobothrium the bothridia 

 surround a myzorhynchus which projects forward from their common base. 

 Anteriorly, this ends in a bluntly -pointed knob. It bears at equal distances four 

 rather leaf-like suckers whose edges are curled inwards, and bear half-way along their 

 edge a pair of inwardly directed projections. 



The bothridia are stalked and in general outline much resemble an ovate leaf. 

 The stalk arises not opposite the suckers in the myzorhynchus, but opposite the space 

 between each pair of neighbouring suckers. The tip or terminal fifth of each 

 bothridium is cut off from the rest by a ridge, and forms a shallow sucker or areola. 

 The edges of the remaining four-fifths are incurved. 



Behind the insertion of these bothridia there is a region which may be called the 

 head ; this does not stain deeply. It contracts and is succeeded by a neck which 

 stains well. In the single specimen from which this description is taken the rest 

 of the body was absent. 



Habitat : Myliobatis maculata, in the spiral intestine. 



Tylocephalum dierama, n. sp. Plate III., figs. 49 and 50. 



Along with Rhoptrobothrium myliobatidis, a specimen or two of what we take to 

 belong to LINTON'S genus Tylocephalum* were found. 



The worms measured between 20 millims. and 35 millims. They were very slender 

 anteriorly, but the posterior proglottides attain a width of 0*5 millim., and the head 

 is about 0*6 millim. in breadth, and is rather longer than broad. 



The head consists of an anterior cushion, called a myzorhynchus by LINTON ; it is 

 obviously to some extent retractile, and in one of our specimens was slightly " pulled 

 in " in the middle, so that the whole head resembled a cottage loaf. This myzorhyn- 

 chus is separated from the second part of the head or " bothrial disk," as LINTOX has 

 it, by a narrow band, not only by a constriction, but by a band. The " bothrial 

 disk " is spherical and bears four equidistant, simple suckers. There is a short neck. 

 The proglottides are, at the posterior end, not more than twice as long as they are 

 broad. They are flattened. Anteriorly they have salient posterior borders, and these, 

 as they approach the hinder end, become much more conspicuous and overhang an 

 eighth or a sixth of the length of the succeeding proglottis. These funnel-like 

 extensions are very characteristic of this species ; they are much less marked in 



* 'U.S. Commission of Fiah and Fisheries,' Commissioner's Report for 1887, Part xv., 1891, p. 805. 



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