Structure of an Ausfralid n Land Leech. 213 



Professor Blanchaid, as quoted by Oka/ divides the Hirudinea 

 into : — 



1. Rhynchobdellidte. 



2. Arhynchobdellidaj. 



Fain. — Gnathobdellidpe. 



Aquatic. — Hirudo, etc. 



Terrestrial. — Ha?madipsa, Xerobdella, Me- 

 sobdella. 

 Fam.^ — Herpobdellidai. 



Aquatic. — -Herpobdella, Trocheta. 

 Terrestrial. — Cyclicobdella, Lunibricobdella, 

 Orobdella. 



According to the characteristics of the genera of the Gnathob- 

 dellidfe, whose members are exclusively terrestrial, the Australian 

 land leech resembles Ha;madipsa more than any of the others. 

 It possesses five pairs of eyes, a point in common with 

 Mesobdella but differing from Xerobdella. Philsemon, however, 

 is unlike these three genera, in that it has but two denticulated 

 jaws. 



In counting the annuli or rings, and fixing the boundaries of 

 the somites of the leech, different workers have adopted different 

 methods. Some begin with the first oculiferous ring on the 

 dorsal surface, others with the first complete ring on the ventral. 

 Oka, in the paper on the Japanese Land Leeches, already referred 

 to, mentions these different methods and adopts Apathy's plan of 

 counting every ring in the body, whether in front of or behind 

 the first pair of eyes, as being the least artificial. He also calls 

 iittention to the fact that "each apparent ring at the anterior 

 extremity of the ))ody has not of necessity the value of one 

 morphological ring." In the present paper I have counted every 

 ring, incomplete as well as complete. The first complete annu- 

 lus is situated immediately behind the fouith pair of eyes (Figs. 

 1, 2 and A), and this, together with the one following it, forms the 

 lower lip of the anterior sucker (B^igs. 1 and A). The complete 

 annuli extend on the ventral surface to the acetabulum (76th 

 annulus), making in all seventy-two complete rings. At the 



1 On Some New Japanese Land Leeches. Journal of the College of Science, Imp. Univ., 

 Japan, Vol. viii., 18%, p. 302. 



