ROME NEW PENTASTOIMTDS. 119 



The hooks are simple and sharply curved. The mouth is pear- 

 shaped with a pointed anterior end. The head is globular and 

 divided from the body by a well-marked neck. The anus is a 

 wide transverse slit on the terminal segment. 



This is a North- American species, but it greatly resembles the 

 Indian species P.pattoni Stephens. The main points of difference 

 are the greater number of rings, P. pattoni having only 36 ; and 

 also the position of the anus, winch is more nearly terminal in 

 P. globicephalus. 



3. Porocephalus bifurcatus Diesing. (Text-fig. 4, A.) 



The identification of Diesing's species is a task of some 

 difficulty, because, as pointed out by Leuckart, he almost certainly 

 described immature specimens. He gives the length of the female 

 as 20-22 mm. and the number of ambulations as 40, though, in 

 the first edition of his Monograph, he figures about 100. This 

 apparent discrepancy may be clue to the fact that in some cases 

 the body contracts in such a way as to make the rings appear 

 double. He also describes the hooks as geminate. 



Among the Pentastomids sent to me from the Zoological 

 Society's Gardens are seven which I take to be P. bifurcatus 

 (text-fig. 4, A) : one is from Boa imperator and six from 

 Coluber melanoleucus. Like Diesing's specimens they are all from 

 the New World, and they agree with his diagnosis, except in so far 

 as regards : — (1) length, (2) number of annulations, (3) geminate 

 hooks. The specimens in question are from about 30 to 40 mm. in 

 length. In most cases the ambulation is obliterated, but in three 

 cases it is visible and the rings number 26, 33, and 37 respectively. 

 The hooks are single. 



But these are exactly the differences which ordinarily occur 

 between immature and adult forms, the geminate hooks especially 

 being a larval character. 



I cannot find any essential distinction between these forms and 

 the African species named P. boulengeri by Vaney and Sambon 

 (text-fig. 4, B), specimens of which I have described in detail in a 

 pa/per to appear shortly. Dr. Sambon points out* that "difference 

 of realm is a powerful argument in favour of diversity of species," 

 but in this case the African and New World species resemble 

 each other so closely that it would seem impossible to distinguish 

 them as separate species f . So that if my identification of the 

 specimens mentioned above with Porocephalus bifurcatus be 

 correct, the African specimens must be regarded merely as a 

 new variety of that species. 



* Trans. Soc. Trop. Med. Liverpool, vol. iii. 1910, pp. 132-140. 



f Text-fig. 4, A, is taken from the specimen from Boa imperator. It appears 

 relatively longer and more slender, but this is only due to greater extension. Tlie 

 specimens from Coluber melanoleucus resemble " P. boulengeri" even more closely. 



