520 Illinois State Laboratory of Natural History. 



prostomium and is less flattened. When exploring, but not 

 swimming, the form is much less depressed and more terete, 

 and may become much more extended and slender. The 

 resting attitudes are varied and interesting. The body may 

 be contracted to an ovoidal form, the upper lip is usually 

 inflected, and the anterior end of the body variously inrolled 

 or folded on the ventral surface. 



Living specimens held in the fingers are so soft and hang 

 so limp that they appear more like pieces of dead tissue than 

 living animals. This peculiarity also enables them to squeeze 

 into the most narrow clefts and thus often to escape from con- 

 finement. None of the cutaneous sense organs are- elevated 

 upon papillae, so that the surface appears perfectly smooth. 



Both living and well-preserved specimens are strongly 

 annulated (PI. XLV., Fig. 24), and in the latter each ammlus 

 is raised into a transverse ridge situated about one third of 

 the length of the annulus from its posterior border. As a 

 result the margins of the body usually appear rather decidedly 

 serrate. In some specimens such elevated ridges extend 

 around the entire circumference of the body. 



The anterior sucker (PI. XLVI., Fig. 34) is mobile and 

 comparatively large, but without any definitely expanded 

 disc. The mouth is large. The upper lip is broad and 

 bluntly rounded, crenulate on the margin, but almost per- 

 fectly smooth and undivided ventrally. Several rows of labial 

 sense organs are situated around its margin and on the pre- 

 ocular and oral annuli. Dorsally the furrows which divide 

 it into annuli may be very faint, but are usually discernible 

 for a portion of its width (PI. XLVI., Fig. 33). 



Of the five pairs of eyes (PL XLVI., Fig. 33) the first three 

 pairs are conspicuous and arranged in a regular arc on the 2d, 

 3d, and 4th annuli; while the fourth and fifth pairs are more 

 widely separated on the 6th and 9th annuli respectively, and 

 are increasingly smaller and deeper and, as a consequence, 

 more obscure. Their optical axes are variously directed ; the 

 first pair forward and slightly outward, the second decidedly 

 outwards and forwards, the third directly outwards, the fourth 

 outwards and backwards, and the fifth backwards and some- 



