480 AUSTRALIAN HIRUDINEA, III., 



that they approach much more closely to Benham's species than 

 to Hirudo australis of Schmarda. 



Length. Breadth. Posterior sucker 

 IIi7'udo australis Schmarda, 72 mm. 16 mm. 10 mm. 



Hirudo mauiana Benham 70 5 4*5 



Limnohdella australis mihi 68 8*5 5 



The total number of annuli is 102, as in species of Hirudo and 

 Limnohdella in general. 



As there are no traces of sensory papillae on the surface, I have 

 attempted, by means of the positions occupied by the nerve- 

 ganglia, to map out the somitic constitution of the animal, taking 

 also into account the assistance given by the position of the eyes, 

 taking for granted that, especially in the middle region of the 

 body, the nerve-ganglion lies in the middle annulus of a somite, 

 and that abbreviation has taken place at either extremity accord- 

 ing to the set plan laid down by Castle's observations. 



Note that, in the newly arranged diagram showing somite-con- 

 stitution, annuli 5,6 and 7,8 show fusion on the ventral aspect. 

 This is of interest, inasmuch as it may very reasonably be con- 

 strued as signifying that the fused annuli belong to one and the 

 same somite. As we find that the number of somites (33) is 

 constant among the Hirudinea in general, it is much more reason- 

 able to conclude that, when abbreviation or extension of the 

 annuli takes place, this is a matter affecting the somite concerned 

 alone. 



