480 Illinois State Laboratory of Natural History. 



visible under a good dissecting lens, though nearly all of the 

 species have been sectioned and the distribution of sensillse, 

 etc., verified in that way. It has also been thought best to 

 omit full synonymical tables (partly because of the doubt 

 which attaches to some descriptions) and to include just 

 sufficient names to connect the species under consideration 

 with the previous descriptive literature. Blanchard's opinion 

 has been followed with regard to the names of European 

 forms. The order in which the species are considered does 

 not express the writer's view of their relationships. The 

 brief notes on habits are the results of observations made 

 chiefly in the neighborhood of Philadelphia, where most of the 

 species occur. 



GLOSSIPHONID^. 



PLACOBDELLA BLANCHAKD. 



Placobdella parasitica (Say). 



Hirudo 'parasitica Say ('24). 



Diagnosis. — Somites I and II are included in the preocular 

 lobe, which may or may not exhibit a furrow separating 

 them ; one pair of small pigmented eyes on the large anterior 

 annulus of III; the furrow ~Val/a2 is much less distinct 

 than Va2/a3; cutaneous warts and papillae are numerous 

 but low and often inconspicuous, and the median series is 

 feebly developed ; the epididymes and ducti ejaculatorii form 

 a close coil chiefly confined to somite XI. 



General Description. — This tortoise leech reaches a large 

 size, occasionally attaining a length in extension of more 

 than four inches. Such huge individuals are, however, rare, 

 and the ordinary examples are seldom more than one half 

 that size. In the resting state the outline is rather broadly 

 oval, the anterior ends being only slightly less broadly 

 rounded than the posterior. The body is depressed, with 

 sharp margins and gently convex dorsum. When fully ex- 

 tended — and the capacity for extension is very great — the 



