The Hirudinca of Illinois. 529 



any papilla, but unlike that species the metameric sensillai 

 are exceedingly difficult to detect, and I am not yet satisfied 

 that they have been correctly identified in surface views. A 

 better developed muscular system gives the body of this 

 species a somewhat firmer consistency. 



The annuli (PI. XLVL, Fig. 28-32) are remarkably 

 distinct, which results chiefly from the presence on each of a 

 strong welt or ridge which encircles it and causes the margins 

 to stand out like so many serra?. Just anterior to the ridge 

 a faint furrow appears on many of the secondary annuli. 



The upper lip (PI. XLVL, Fig. 29, 32) is rather slen-der 

 and pointed and its ventral surface divided by a slight 

 median and several lateral longitudinal grooves. The mouth 

 and sucker are relatively smaller than in the horse-leech. A 

 slight constriction is usually evident between the fourth and 

 fifth pairs of eyes. The eyes (Fig. 28) are arranged as in 

 //. uutnnordtis. 



Very few examples exhibit a well developed clitellum, but 

 when present it has a form and extent similar to that of 

 H. ))i((rinor((tis. Although the male and female pores are 

 situated on the annuli homologous to those bearing them in 

 H. marmoratis, two more annuli intervene between them and 

 the anterior end than in that species. This results from the 

 presence of an additional annulus in each of somites VII and 

 VII I, The orifices are also situated further eaudad on their 

 respective annuli (though seldom beyond the middle) than in 

 that species. 



The usual seventeen pairs of nephridiopores (PI. XLVL, 

 Fig. 29) are situated on the annulus I?'! of somites VIII to 

 XXIV inclusive. As in H. marmoratis they open just pos- 

 terior to the transverse ridges, which at each pore are pushed 

 forward as short spout-like projections w^hicli may serve to 

 direct the flow of the excreted fluid. The distance separating 

 the two pores of a pair is almost exactly half the width of the 

 body at that point. ^ 



Anniili and Somites. — Owing to its distinctness the annula- 

 tion (PI. XLVL, Fig. 28-32) is very easy to work out, but 

 on account of the difficulty or impossibility of detecting the 



