422 iMr. H. A. Baylis on a remarkable 



otlier at the invagination. Tims tlie neck is lined by a tliin 

 cuticle, which is followed by two layers of muscles — tlie inner 

 coat circular, the outer longitudinal. Outside the lonoitu- 

 dinal muscles there is a coat of parenchymatous tissue, with 

 very densely crowded nuclei on the inner side. The outer 

 boundary of this layer, like the inner boundary of the wall of 

 the bladder, is vaguely defined, and the parenchyme-cells 

 seem to be bathed in the fluid contained in the bladder, 

 which in the fixed material has become coagulated into a 

 flocculent mass, containing numerous refringent granules. 



Systematic Position. 



The structure of the scolex enables the affinities of thi-^ 

 larval form to be decided with some precision. It may be 

 assigned definitely to the genus Monori/pma, Diesing, 1863, 

 of the family Phyllobothriidte. The question therefore arises 

 whether it can be specifically determined. The worms of 

 this genus, of which six species appear to have been described 

 up to the present, are all parasitic, in their sexual stage, in 

 sharks and dogfish. 



The six known species are the following : — 



1. 31. perfectum (van Beneden, 1853) lAnthobothrium per- 



fectuii{\. 



Host : Lcemargus horealis. 



2. M. gracile (Olsson, 1869) \_Triloeulana gracilis]. 

 Host : Acanthias vulgaris. 



3. M. elegans, Monticelli, 1890 [originally described by 



Zscliokke, 1889, under the name of Monorygma per- 

 fection^ Diesing], 



Hosts : Scyllium cattdus and S. stellare. 



4. 31. chlamydoselachi, Lonnberg, 1898. 

 Host : Chlamydoseltichus anguineus. 



5. M. dentatum, v. Linstow, 1907. 



Host : a shark (Antarctic) of unknown determination. 



6. M. rotundum, Klaptocz, 1907. 

 Host: Xot'idamis \_Hexanchus\ griseus. 



