l82 AQUATIC MICROSCOPY FOR BEGINNERS. 



a. Back smooth and naked, or transversely furrowed 



or bearing small, hemispherical elevations, 

 Icthydium. 2. 



b. Caudal prolongations much shorter than the. 



body, not segmented nor ringed; dorsal scales, 

 when present, rounded, ChcBtdnotus. j. 

 b. Caudal prolongations long, ringed or segmented, 

 often curved; scales rhomboid or diamond- 

 shaped, Lepidoddrma. 4. 



■ III. (i). Dasydytes sAltitans (Fig. 136). 



In contour this lively creature remotely resembles 

 Chatonotus (Fig. 134), but differs in a shorter, more 

 chubby body, in 'the presence of a more distinctly 

 formed neck, but especially in the absence of a furcate 

 caudal extremity. The body is colorless and trans- 

 parent. Its internal structure is not very widely dif- 

 ferent from that of Chaetonotus, but in general ap- 

 pearance the animal lacks the graceful form and the 

 attractive movements of the Chaetonotus. The pos- 

 terior extremity is simply rounded or truncately con- 

 vex. Its movements are much less smoothly gliding 

 and facile. The habitat of both genera is the same, 

 being chiefly near the bottom of shallow ponds. 



The head is distinctly three-lobed, the frontal lobe 

 being the smallest and bearing on its anterior border a 

 colorless, apparently chitinous plate or cephalic shield. 

 Both surfaces of the head are ciliated, the cilia being 

 very long and fine, and arranged in two distinct, 

 transversely encircling series, the posterior row pro- 

 jecting and vibrating anteriorly, while the anterior 

 series projects and vibrates posteriorly. 



The neck is about as long as the head, sometimes 



