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THE AMERICAN NATURALIST [Vol. XLII 



examples of the forms mentioned. It is more than 

 usually contractile and therefore difficult to preserve in 

 a suitable condition for study. The outline is very char- 

 acteristically pyriform and strongly convex dorsally, as 

 shown in the figures. But the most striking peculiarity 

 is the attenuation of the posterior somites to form a 

 narrow pedicel just in front of the posterior sucker, 

 which consequently stands out freely in a most char- 

 acteristic manner. The oral sucker has the same struc- 

 ture as in P. parasitica. 



No trace of cutaneous papillae can be detected, the skin 

 being perfectly smooth. The segmental sensillae and 

 scattered sense organs are very indistinct. Eyes are 

 very difficult to detect in the mature animals, but appear 

 as small pigment masses at III-IV in the young. The 

 annulation is essentially like that of P. parasitica except- 

 ing the caudal peduncle and the generally simpler struc- 

 ture of the corresponding somites of P. parasitica. 



Somites I and II contain each but one annulus. 

 Somites III and IV are biannulate and V is biannulate 

 dorsally, but ventrally the furrow fades away medially. 

 VI is triannulate above, but the furrow al-a2 is incom- 

 plete below. Somites VII to XXIV are triannulate, but 



