256 MICROSCOPY FOR BEGINNERS. 



carried on the back under the shell. The animals are 

 flesh color. 



14. ESTHEIUA. 



The shell is smooth and shining, and marked with dis- 

 tinct lines running almost parallel with the front, or 

 free edge, of the valves. It is very thin, flat, and large, 

 measuring about two-thirds of an inch in length. The 

 males have two pairs of hands, or one on each of the 

 four front legs. The shell of the several species varies 

 from oval to oblong with the upper margin very much 

 flattened, or it may be somewhat globose. Most of the 

 species are confined to the waters west of the Missis- 

 sippi River, one, however (Estheria Mexicdna\ being 

 found near Cincinnati. Many of them are in appear- 

 ance not unlike a small clam, or the little fresh-water 

 mollusk, Pisidium, so common almost everywhere. 



15 ARTEMIA (Fig. 169). 



Artemia occurs only in brine or the water of salt 

 lakes. It is not rarely found in the hogs- 

 heads of water on railroad bridges or tres- 

 tles, where the water is made salt to pre- 

 vent freezing. The bodies are slender 

 and pale red, flesh -color, or sometimes 

 greenish. The feet are eleven pairs, beau- 

 tifully fringed with many long hairs, and 

 P5 169 Artomia Bearing the flattened branchial or breath- 

 (a female). ing-plates. When the creature swims on 

 its back, as it habitually does, these feathery feet beat 



