2G2 ' CKYLON MARINE lUOI.OUICAL IIKJ'ORTS. 



(.'omparative rarit_\- of tlio parasites point to tlio fact that ElasmobraiK-hs suffer little from the presence of 

 cestodes, though doubtless the Teleosteans, in whose bodies for the most part the worms pass through 

 the cystic stage . suffer considerably. When . however , they do occur in Elasmobranchs , tliey are often met 

 with in gi'eat numbers, and this is ospocially the case with the genus Calliobothrium, which is sometimes 

 found in enormous numbers on the spiral valve." 



This hardly' agrees with my exi)erience on tlie Ceylon pearl banks. So far as I have observed, 

 the cvstic stages verv often occur in various molluscs and crabs, and are by no means limited to 

 smaller fish. 



Cephalobolhrium ahrwptum, Southwell, and Cepfuilobothrium variable, SouthweU, measured respec- 

 t ively 12 and 13 cms. \\hon jireserved (23). Rliinebothrium ceylonicwm, Shipley and HorneU, and Prosthe- 

 robothrium injgonii^, Sliiploy and HornoU, measured 12 and 23 cms. (20). Cestodes of tliis length are, 

 however, not very common. Ninety-nine per cent, of the Elasmobranchs I have examined, and they 

 nimiber many liundreds, were infected, and I have not noted that the parasites obtained tlierefrom were 

 always smaller and more numerous than those obtained from smaller members of this family. 



PLATYBOTHRrrM, Llnton (11). 



Body articulate, tseniaeform. Head decidedly flattened, squarish, or trapezohedral. Bothria 

 four, subtriangular, sessile, arranged in marginal pairs, armed with compound hooks, and each terminating 

 l)osteriorly in a cup-like depression or loculus. A single indistinct circular depression (supplemental disc ?) 

 on each bothrium in front of hooks. Genital pores marginal. (Linton.) 



Platybothrium spinuUfera, n. sp. (Plate I.. Figs. 4, 5, 6, and 7.) 



Average Measurements. 



Extrenae length . . . . . . 33 mm. 



Length of head . . . . • 4 mm. 



Breadth of head . . . . . . . . • 5 mm. 



Length of terminal proglottid .. .. .. '8 mm. 



Breadth of terminal proglottid . . . . . . ■ 6 mm. 



The head is provided with four sessile bothridia, wliich are arranged laterally. Thus tlie head in 

 transverse section is oblong, with two bothridia on each of the larger sides of the rectangle. The bothridia 

 are divided by a transverse sej)tum into two locuH, and the 2)voximal one is twice as large as tlie distal one. 

 The edges of the bothridia are indented at the junction of the septa, and in the posterior loculus they are 

 somewhat incurved, so that the loculus a])pears slightly i)ocket-shaped. Both locuh are deeply concave. 

 On carefuUy examinuig each bothridium, it was found that in a few specimens there was a very faint 

 indication of a second septum dividing the posterior loculus into two, and resulting in the bothridium 

 aiipearing to have three locuh, whilst the rest of the three bothridia composing the head on the same 

 individual bore no indication whatever of a second septum. 



Each bothridium is surmounted by two hooks, each of which is strongly bifurcated and curved. 

 The prongs or forks of the hooks are usually unequal in size. Where the prongs run into the basal part, 

 there is often a blunt projection given off in another plane, which appears as a thick dwarf process, but 

 it is not always present. The pair of hook.j on each bothridium, which are situated on the middle Une of 

 the longer side of the scolex (when the latter is viewed in cross section), are shghtly larger, and have a 

 much longer subcutaneous basal trunk than those hooks which when viewed similarly are situated at 

 the corners. The hooks on each botlu'ieliuni are, therefore, not symmetrical. The basal parts of the two 

 pairs of bifurcated hooks on each bothridium are widely separated from each other, and there is no 

 intermediate bar or connecting piece which joins them, such as is figured by Lmton (11) in Platybothrmm 

 ccrmnum. The hooks are aU characteristically hollow. 



Each bothridium is surmounted by a fairlj' large accessory sucker, the greatly thickened walls of 

 w hich together form a squarish pad at the anterior extremity of the head. Linton refeis to his specimen 

 of Platybothrium cervinum as havuig " a single indistinct circular depression (supplemental disc ?) on each 

 bothrium in front of the hooks," but in our specimens this accessory sucker is remarkably well defined. 



