No. 500] PLACOBDELLA PEDICULATA 531 



the furrow al-a2 is incomplete medially on the ventral 

 side of both VII and VIII, and in most of the succeeding 

 sonites is less marked than either a2-a3 or the inter- 

 segmental furrows. In the anterior somites and to a 

 less degree in the posterior, a3 is slightly longer than 

 al or a2. The annulation of the post-anal somites, con- 

 stituting the caudal peduncle, is irregular and somewhat 

 puzzling on the older specimens, but is fairly distinct on 

 the younger ones. Somite XXIV, which immediately 

 succeeds the anus, is triannulate. Somites XXV, XXVI 

 and XXVII are all biannulate, but al of somite XXV is 

 partially divided and al of both XXVI and XXVII is 



larger than a2. Neither annulus of XXVII is complete, 

 al reaching only to the sides of the body and a2 not as 

 far. The disc is composed of somites XXVIII to 

 XXXIV. The accompanying Fig. 3 represents the 

 arrangement of the furrows in a young animal. Somite 

 XXIV is the last segment of the body proper and its 

 posterior boundary forms in contracted specimens a fold 

 which envelops the contiguous portion of the narrowed 

 peduncle. The latter continues to narrow to the sucker, 

 to the middle portion of which it is strongly attached for 

 rather more than the posterior half. The posterior 

 sucker is larger, circular and directed strongly ventrad. 

 The nephridiopores are in the sensory annuli of somites 

 VIII to XI and XIII to XXTII and are placed similarly 

 to those of P. parasitica. 



