500 Illinois State Laboratory of Natural History. 



nephridiopores have been determined on somites VIII to 

 XXIII inclusive. 



The posterior sucker is exactly circular, with a finely but 

 distinctly denticulated margin. It is, though not of large 

 size, widely exposed behind, and reaches anteriorly to XXIII 

 a\. Its pedicle of attachment is unusually small, permitting 

 great freedom of movement. 



Annuli and Somites (PL XLIL, Fig. 5). — I forms the apex 

 of the head and is divided dorsally into two small rings by a 

 cross- wrinkle. 



II is quite distinctly biannulate and bears evident dorso- 

 median and dor so-lateral sensillre. 



III consists of two large annuli, of which the anterior is 

 slightly divided by a faint cross-furrow which is confined to 

 the median region. It bears the eyes, which are separated 

 by a space about equal to their own diameter, and three pairs 

 of sensillae, one of which is remarkable by reason of its 

 position directly above the eyes. Sections of this species 

 have not been studied. 



IV closely approaches the triannulate condition, a 1 having 

 very nearly the typical relations. Three or sometimes four 

 pairs of sensilla? are easily discernible. 



V. This somite presents several interesting features. It 

 consists of two annuli of about equal size, both enlarged at 

 the margins, where the anterior one is somewhat divided into 

 a 1 and a 2. Three pairs of sensillse are present on a 2, but the 

 dorso-medians are wanting, while on a 3, almost directly 

 behind the dorso-laterals, appear what seem to be an extra 

 pair of these sense organs. 



VI is also peculiar in that al is completely divided on the 

 dorsal side into two small annuli which appear as one 

 ventrally. 



VII is fully triannulate and the annuli present the typical 

 proportions. ^41 is the smallest, a 2 intermediate, and a 3 

 the largest. A 1 and a 3 exhibit shallow ventral furrows across 

 their entire width, and the furrow of a 3 continues on to the 

 dorsal side, from the margin almost to the dorso-lateral 

 carinas It cuts the annulus posterior to the sensillre. XXII, 



