442' Proceedings of Royal Society of Edinburgh. [skss. 
named Pchinorkynchus antarcticus , n. sp. Its distinctive features 
are, specially, the form of the body and the distribution of spines 
upon it ; the size and shape of its rostrum, and the size, form, and 
number of its hooks ; the characters of the sub-cuticle ; the 
arrangement and distribution of the lacunae ; the relative sizes of 
the sexes ; the size of the shelled embryos, and the number of the 
testes. Of the foregoing, the form of body and distribution of 
spines upon it are more especially adaptations, as already suggested, 
for more secure fixation upon the host ; and possibly, in the case of 
the male, which shows some degree of flattening, in addition the 
spines upon this flattened area are of service in locomotion. These 
features are readily understood as modifications (acquired by 
natural selection) of a symmetrical type with uniformly distributed 
