The Hirudinea of Illinois. 487 



Placobdella rugosa (Vekrill). 



Clepsine ornata var. rugosa Verrill CIA). 



Diagnosis. — Somites I and II distinctly and completely sep- 

 arated, usually strictly uniannulate ; the single pair of eyes 

 very close together on the posterior part of the large annulus 

 of III ; the furrow V alja 2 quite as distinct on the dorsal side 

 as V a2/a3 ; cutaneous papillae numerous, mostly very large 

 and rough and the median series very conspicuous ; repro- 

 ductive organs essentially as in P. parasitica. 



General Description. — Although reaching a large size the 

 largest individuals probably do not equal the largest of 

 P. parasitica. Generally the length is from one to two 

 inches. When resting this is the broadest and flattest of 

 our leeches, the whole body being excessively depressed and 

 foliaceous. A living individual in this state measures twenty- 

 two millimeters long by fourteen broad. Incapable of the 

 great degree of extension possible to P. parasitica it never 

 becomes very slender. 



The integuments have a peculiar translucent appearance, 

 quite different from the opacity of P. parasitica. The whole 

 dorsal surface of the body is exceedingly rough, in large living 

 examples being clothed with a veritable forest of papilla? from 

 which the eye readily picks out three longitudinal series of 

 more prominent ones, conspicuous not only because of their 

 large size but because of the regularity and constancy of their 

 occurrence. One of these is median, the others about half- 

 way to the margin. Toward the anterior end they become 

 smaller and fewer ; at the posterior, the median series ceases 

 and several very prominent papillae appear in a short series 

 on each side of the median line. Further details are given 

 below under the description of a typical somite. 



Under all conditions of contraction or extension the anterior 

 sucker partakes of the regular curvature of the body and never 

 appears as an appreciably expanded disc. In preserved spec- 

 imens it is deeply concave, with a high but thin posterior 

 margin formed by IV, and thicker lateral margins. Anteriorly 

 the preocular lobe is rather narrow and more or less inrolled 



