THE LEECHES OF MINNESOTA 35 



DESCRIPTION. * 



Plate C, Figs. 1, 2, 3 and 4. 



Like Placobdella parasitica and P. rugosa this is a species of large 

 size, thongh not quite equaling the largest examples of the forms 

 mentioned. It is more than usually contractile and therefore dif- 

 ficult to preserve in suitable condition for study. The very char- 

 acteristic pyriform outline and strongly convex dorsum are evident 

 from the figures, but the most striking peculiarity is the attenua- 

 tion of the posterior somites to form a narrow pedicle just in front 

 of the caudal sucker, which consequently stands out freely exposed 

 behind the body in a most characteristic manner. The oral sucker 

 has the same structure as in P. parasitica. 



No trace of cutaneous papillae can be detected, the skin being 

 perfectly smooth, and 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 

 excepting the caudal peduncle and the generally simpler structure 

 of the corresponding somites of P. parasitica. 



Somites I and II contain each but a single annulus. Somites 

 III and IV are bi-annulate and V is bi-annulate dorsally but ven- 

 trally the furrow fades away medially ; VI is tri-annulate above, 

 but the furrow al/a2 is incomplete below. Somites VII to XXIV 

 are tri-annulate but the furrow al/a2 is incomplete medially on the 

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

 somites is less marked than either a2/a3 or the inter-segmental fur- 

 rows. In the anterior somites, and, to a less degree, in the posterior, 

 a.3 is slightly longer than al or a2. The annulation of the post-anal 

 somites, constituting the caudal peduncle, is irregular and somewhat 

 puzzling on the older specimens, but is fairly distinct on the young- 

 er ones. Somite XXIV, which immediately succeeds the anus, is 

 tir-annulate. Somites XXV, XXVI and XXVII are all bi-annulate, 



*This description is based upon both young, and large, mature speci- 

 mens gorged with blood. In view of unavoidable delay in the publication 

 of Professor Nachtrieb's projected report on the Leeches of Minnesota, 

 Piofessor .Moore kindly consented to the free use of his description em- 

 bodied in the systematic portion of this report. I have retained the specific 

 name suggested by Moore, though his description, being based upon a 

 single large, gorged and much contracted specimen was of necessity some- 

 what incomplete. 



The original description wafe published in The American Naturalist, 

 Vol. XLII, August. 1908. 



