176 SPOLIA ZEYLANICA. 



Trhtomum. 



Body ovate or circular, flat, with two round suckers in front and 

 a large, disc-shaped posterior sucker with seven rays and small 

 rods ; cerebral commissure with four ocelli ; genital orifices and 

 vagina in front on the left ventral side; testes numerous: ecto- 

 parasitic on the gills and surface of the body of marine fishes. 



38. — Tristmnum megacotyle, n.sp. 



PI. I., figrs. 19-20. 



From the surface of the body of a sword fish, Histiophoru'i, sp.; 

 Beruwala, February 5, 1904. 



Length 7*5, breadth 6 mm. ; ventral cuticle, except on the 

 suckers and head, thickly beset with circular papillae, measuring 

 0"31 mm. 



The two anterior suckers are equal to I of the body length; 

 the caudal sucker has a diameter equal to ^ the body length, and 

 shows seven radial ribs (pi. 1, fig. 19) which abut upon a central 

 roundish area produced backwards ; the sucker is bounded at the 

 peripheryby a striated border; in the posterior region of the sucker 

 there are two straight undivided rods attenuated at the ends, 0*48 

 mm. long ; these rods are always described as hooks in the defini- 

 tion of the genus Tristomum, but they do not deserve this name 

 since they do not serve for attachment, but, on the contrary, for 

 releasing the sucker from its adhesion, assuming a vertical posi- 

 tion by the action of special muscles for this purpose. 



A similar, though much larger species, also living upon Histio- 

 phorus, is TrLsfmnum fa^vr,Yevri\l = T)-.ovafe,Goto; the length of 

 this species amounts to 13 mm. and its breadth 12 mm. ; the 

 diameter of the anterior suckers equals I of the body length ; the 

 rays of the caudal sucker are narrow, its margin is unstriated, 

 and the rods are expanded and irregularly laciniate at the 

 roots. 



Cf. S. Goto, Studies on the Ectoparasitic Trematodes of Japan. 

 Journ. Coll. Science, Japan, VIII., part 1, Tokyo, 1894, pp. 

 241-244. 



IV.— CESTODA. 



Hymenolepis. 

 Tseniids with armed scolex ; proglottids generally broader than 

 long ; genital orifices marginal and unilateral ; in each segment 

 three testes ; the mature uterus completely fills the proglottids ; 

 parasitic in mammals and birds. 



