258 THE SCOTTISH NATURALIST 



4. Most interesting of all is the question suggested as to the 

 phylogenetic position of these three genera. Mackayia, 

 Giebelia, and Philocea?ius are complicated forms in a group 

 where the general note is one of severe simplicity. Their 

 respective hosts belong to an ancient stirps of the Bird 

 Kingdom. The life conditions of these parasites must have 

 been long unchanged, to a degree remarkable even in an 

 order noted for the constancy of the environment of its 

 members. Giebelia, Mackayia, and Philoceanus must 

 therefore be first beginnings or amongst the last expressions 

 of Philopterid evolution. According to Professor Kellogg's 

 interpretation of the developmental history of the order, the 

 latter alternative must be accepted. 



Explanation of Figures. 



1. Head of £ . 4. Genital mark, g . 



2. Sternal marks of £ . 5. Head of <j? . 



3. Terminal segments, ^. 6. Genital mark, $ . 



A NEW SPECIES OF MACK A YIA 

 {M. HETERACANTHUS). 



By James Waterston, B.D., B.Sc. 



While the foregoing article was in the press, the writer 

 had submitted to him, by Dr Peringuez, director, Cape 

 Town Museum, a still more remarkable form of the same 

 genus. The types of this new species will be fully described 

 later. Meanwhile, for the benefit of students of the group, 

 the following notes may be given : — 



a. Third joint of £ antenna with appendage. Head in both 

 sexes bearing four short, heavy, peg-like spines. Host, 

 Puffinus anglorum. M. dimorpha, Waterst. 



a. a. First and third joints of & antenna with appendages. Head 

 in both sexes bearing two bristles and two heavy spines, 

 arranged as in dimorplia, the bristles being in the place 

 of the anterior pair of spines. A slightly larger form 

 than the preceding. Host, Procellaria gigantea. 



M. heteracanthus, sp. no v. 



