528 Illinois State Laboratory of Natural History. 

 Hsemopis lateralis (Say). 



Hirudo lateralis Say ('24). 

 Macrobdella valdiviana Philippi ('72). 

 Semiscolex terreslris Forbes ('90). 



Diagnosis.— VII 65 and b 6 and VIII b 1 and b 2 are fully 

 developed, so that VII is quadriannulate and VIII quinque- 

 annulate. The male pore is on annulus 34 (XI b 6), the 

 female on 39 (XII b 6) ; the vagina and atrium extend to the 

 anterior part of XIV ; the ovaries lie between the female 

 pore and ganglion XII. 



General Description. — Many of the characters of this large 

 leech have been described by Forbes ('90). It reaches a size 

 much larger than H. marmoratis, some examples of the 

 terrestrial variety from Illinois measuring as contracted 

 alcoholic specimens nearly 8 in. in length and f- in. wide. 

 The smallest specimen in the collection measures 38 mm., 

 the largest 190 mm., in length. A medium-sized individual 

 from which the drawings were made, measures : — 



Total length, ....... 



Length to c? pore, ..... 



Width at d pore, ...... 



Greatest width (just anterior to 17th nephridiopore). 

 Width at anus, •. . . . . about 



Diameter of posterior sucker, 



Depth at d pore, ..... about 



Depth at last nephridiopore, . . 



Depth at anus, ...... 



Living aquatic examples which I have watched assume the 

 attitudes and shapes described for H. marmoratis, but 

 H. lateralis is much more slender and capable of much 

 greater elongation. The greatest width is further back 

 (about XXIII), from which point the body tapers gently 

 forward. Compared with //. marmoratis the ventral surface 

 seems flatter, the dorsal more abruptly, but still gently, 

 arched, and the anterior region more terete. As in that 

 species the surface of the body is perfectly smooth, without 



