488 Illinois State Laboratory of Natural History. 



ventrally, where it is continuous with a thick rounded ridge 

 which extends to about the middle of the sucker and ends at 

 a deep curved furrow continuous laterally with III/IV. The 

 mouth is a minute pore placed near the anterior end of the 

 ridge beneath the overhanging preocular lobe. Metameric 

 sensillffi on the preocular region have not been detected in 

 surface view, though they can be demonstrated readily enough 

 in sections. The eyes are essentially as in P. parasitica. 



No clitellum has been found. The male sex pore is at XI/XII 

 and the female at XII a2/a 3, but a 3 is enlarged mesially and 

 pushes forward into an emargination in a 2, so that the female 

 pore generally lies rather more within the latter. The male 

 orifice is the larger and is surrounded by more or less promi- 

 nent rugosities. The most anterior nephridial openings which 

 have been detected are on VIII, the last on XXIII. 



Although of smaller size than in P. parasitica the posterior 

 sucker is rather large and has a longitudinal diameter slightly 

 exceeding the transverse. It extends anteriorly to XXIII. 

 The entire free dorsal surface bears papillse which are nu- 

 merous and rough on the posterior exposed part, where four 

 to six radiating rows are larger than the others. Anus 

 XXYII/XXYIII. 



Annuli and Somites (PI. XLIL, Fig 2). — I and II consti- 

 tute the preocular lobe. 



III is biannulate, with the large anterior ring very faintly 

 divided by an incipient cross-furrow, posterior to which are 

 the closely approximated eyes, two pairs of metameric sen- 

 sillffi, and one pair of warts which apparently belong to the 

 dorso-lateral series. The second annulus bears a full set of 

 the characteristic papillae or warts, but they are of very small 

 size. 



IV differs from III dorsally in that a 1 is more distinctly 

 differentiated from a 2 by a furrow which is always distinct 

 marginally but may disappear mesially. The anterior annu- 

 lus (a 1) thus indicated is smaller than a 2, and bears no 

 papillae except in the case of two exceptionally rough indi- 

 viduals from Tinicum Island, near Philadelphia. The a 2 

 constituent bears all of the dorsal sensillfe except the dorso- 



