The Hirudinea of Illinois. 499 



cler and less flattened and foliaceous than in other glossiphon- 

 ids of equal size. It is never very wide and depressed, but on 

 the contrary rather strongly convex dorsally. Capable of 

 great extension and contraction the body may become very 

 slender, especially anteriorly, or short, thick, and elliptical, 

 and very convex above. In both states the head stands out 

 clearly and sharply as a distinct region. This is an excellent 

 character for distinction from the other leeches described 

 in this paper. 



Viewed from above the head is very broadly cordate, the 

 bluntly rounded apex being anterior. Below, the very free 

 posterior margin is entire and slightly convex or straight. 

 This margin appears to be formed by the very strong down- 

 ward and backward development of V, which becomes much 

 enlarged below and whose ventral sensillre are visible on the 

 lateral parts of the posterior margin of the sucker. Dorsally 

 the surface of the head or sucker is strongly annulated. At 

 the margins the annuli are supplemented by a narrow but 

 distinct undivided rim. The ventral surface is smooth, with 

 sometimes two or three faint transverse furrows. -Just inside 

 of the anterior border is the small mouth, apparently in II. 

 The labial sense organs are exceptionally well developed 

 around the entire margin of the sucker. 



The posterior limit of the head is clearly defined both above 

 and below by the furrow V/VI. This is followed by two small 

 annuli (which are regarded as a divided VI al) which form 

 a short neck embraced anteriorly and concealed below by 

 V a 3. Ventrally they become still smaller and perhaps 

 united. Posterior to this point the body increases rapidly in 

 width and the posterior part of VI is equal to IV, the widest 

 part of the sucker. 



The most striking characteristic of the species, however, 

 is the presence of three prominent carinse which extend from 

 just behind the head to the posterior sucker. These are 

 formed chiefly of high and closely appressed papillae, the tips 

 of which produce a sharp erect serrate crest. 



There is no true clitellum, and the genital pores have the 

 usual situations at XI/XII and XII a Z/a 3. Sixteen pairs of 



