CASTLE : NORTH AMERICAN RHYNCIIOBDELLID^. 21 



4. Eyes six, the first pair small and close together, the others 

 farther apart ; rings without metameric markings, or with dark 

 pigment on the anterior ring of each somite. 



G. heteroclita (p. 42) 

 Crop diverticula seven pairs ; male and female genital pores separated 

 by two body rings. 



5. Eyes six, distinct, in two parallel rows ; a conspicuous longi- 

 tudinal baud of dark pigment on either side of the median plane 

 dorsally, and a fainter one ventrally ; inconspicuous papillae on 

 the dorsal surface G. elegans (p. 4G) 



6. Eyes apparently a single pair, far forward on the head and 

 confluent; back distinctly papillose. A large species, often foimd 

 on turtles G. parasitica (p. 51) 



IV. DESCRIPTION OF SPECIES. 

 1. Glossiphonia stagnalis Linn^us (1758). 



Plate 1, Figs. 1, 3; Plate 3, Fig. 4; Plate 3, Figs. 7-10, 13; Plate 8, Fig. 34. 



Ilirudo stagnalis Linnaeus (1758) ; H. bioculata O. F. MuUer (1774) ; Clepsine 

 bioculata Savigny ('20); C. modesta Verrill ('72); C. submodesta Nichol- 

 son ('73). 



a. Habitat, Form, Size, Color. 



This species is found in Europe, the adjacent parts of Asia and Africa, and 

 in North and South America. As one might expect in the case of so cosmo- 

 politan a form, much has been written about it, but its external morphology 

 has never been carefully and accurately analyzed, and published accounts of its 

 internal anatomy contain a number of errors or omissions, some of which 1 

 hope to rectify. 



The general form of the body as seen in dorsal view, when partially extended, 

 is shown in Figures 1 and 4. The body is broadest posterior to its middle and 

 thence tapers gradually toward both ends. The head, which is only slightly 

 wider than the neck, is evenly rounded in front (Figure 3) ; dorso-ventrally 

 the body is very much flattened, especially when at rest. The animal is very 

 active in its movements and can greatly elongate its body so as to become more 

 than ten times as long as it is broad. The largest individuals measure as 

 follows : — 



Length, fully extended, 20-25 mm. ; at rest, 8-10 mm. 



Width, fully extended, about 2 mm.; at rest, about 5 mm. 



Color, flesh-color or grayish. Small individuals are usually quite clear and 

 transparent, but larger ones are apt to be more or less opaque. This opacity. 



