CASTLE: NORTH AMERICAN RHYNCIIOBDELLIDiE. 39 



as seen in a lateral view is shown in Figure 14, cb. It lies for the most part 

 in somites vii. and viii. This is about a somite posterior to the usual position 

 of the brain in G. stagnalis (Figures 4, 7). 



The number of fused ganglia represented in the brain is, as in G. stagnalis, 

 six, and the nerve capsules have the same general arrangement as in that 

 species. The ventral capsules of ueuromeres il.-v. are placed side by side, 

 while those of neuromere vi. lie one behind the other (Figure 18 ; compare 

 Figure 10, Plate 3). The six capsules of neuromere i. are situated well dorsal, 

 as in G. stagnalis, and the supra-oesophageal connective is pushed back nearly 

 over the middle of the entire brain mass (Figures 14, 16). The lateral cap- 

 sules of neuromere il. are shown in the dorsal view (Figure 16) ; those of neu- 

 romeres iii.-vi., in the ventral view (Figure 18). 



In Figure 14, which represents a parasagittal section, is shown the position 

 of the paramedian sensillae of the head somites, certain of which also appear 

 in Figure 15. These indicate clearly the sensory rings of the somites in that 

 region, and so aid in the determination of the external limits of the somites. 

 The eye is clearly derived from one of the segmental organs of somite m. 

 (ring 2), as the position of its nerve indicates. This view is conhrmed by a 

 comparison with the conditions existing in G. heteroclita and G. elegans. 



3. Glossiphonia elongata sp. nov. 



Plate 6. 



a. Habitat, Form, Size, Color. 



This leech first came to my notice in September, 1898. While collecting 

 G. stagnalis from Spy Pond, near Cambridge, I found three or four leeches 

 which, although of about the same size as stagnalis and occurring in similar 

 situations, at once attracted my attention because of their more slender bodies 

 and the peculiarities of their movements. These animals were carefully pre- 

 served, and diligent search was made the following spring for more. This 

 search, however, was fruitless ; but in September, 1899, I was fortunate enough 

 to find quite a number of individuals in a pool near Fresh Pond, Cambridge, 

 some of which I have since kept alive in aquaria for several months. 



The body is less flattened dorso-ventrally in this species than in any other 

 Glossiphonia known to me, being sub-cylindrical in cross-section. It is ex- 

 tren\ely slender, even when contracted, and both head and acetabulum are 

 small (Figure 27, Plate 6). This species does not roll itself into a ball, as 

 other species do, when disturbed. Instead, it writhes about or twists itself 

 into knots like an earthworm. In aquaria it moves little from place to place, 

 but, attached by its weak posterior sucker, extends its snake-like body searching 

 hither and thither as for a place of concealment, or, losing its attachment, seems 

 unaljle to regain it and writhes helplessly like an earthworm on a smooth 

 surface. 



The largest individuals which I have examined measure as f(.)llows : — 



