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FRESH-WATER BIOLOGY 



10 (7) Body covered with hemispherical papillae. 



Lepidoderma concinnum (Stokes) 1887. 



Length o.og6. Body cylindrical. Back and sides covered with 

 small half-round papillae arranged in thick-set oblique rows. Egg 

 smooth, o.oss mm. long. New Jersey. 



Fig. 969. Posterior region of Lepidoderma concinnum in dorsal view. 

 X about 52s. (After Stokes.) 



11 (2) Body provided with spines either attached to the dermal scales or 



springing directly from the surface. 



Family Chaetonotidae . . 12 



12 (30) Caudal process simple; spines attached to dermal scales. 



Chaetonotus Ehrenberg 1830 . . 13 

 A large and complicated group; more than forty species already described; ten species re- 

 ported from North America by Stokes. 



13 (20) Dorsal spines nearly uniform in length, at most twice as long on 



posterior region as on anterior region, and without any 

 marked transition from one size to another 14 



14 (15) Dorsal spines with accessory barbs or points. Anterior region 



sharply set off from so-called "neck." 



Chaetonotus similis Zelinka 1889. 



Length of body 0.12 to 0.22 mm., of esophagus 0.05 mm. Body 

 covered dorsally and laterally with triangular scales carrying spines 

 with accessory point. Oral funnel plicate. Originally described 

 from Trenton, New Jersey, as Ch. maximus which it closely 

 resembles in head and body. Under a high magnification differ- 

 ences in the spines appear. All of them are forked and have 

 a fine lateral point near the tip. 



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Fig. 970, Chaetonotus similis in dorsal view. X 375. A, body spine 

 from the side. X 1600. (After Zelinka.) 



