272 FRESH-WATER BIOLOGY 



11 (lo) Tentacles short, few in number, extending from about the mouth. 



Mesodinium Stein. 

 Representative species. 



Mesodinium pulex Claparede and Lachmann 1858. 



Body turbinate, conical, and tapering anteriorly. A wreath of strong cilia on 



a constriction halfway between the middle of the body and the base of the 



-jr/ , 1 1 1 V v^ snout-like proboscis. According to Claparede and Lachmann three long stylate 



^// W V\ processes e.xtend in front of the mouth. Length 15 /i. Habitat, reported by 



Claparede and Lachmann, salt water. 



Fig. 461. Mesodinium pulex. X 8io. (After Kent.) 



12 (7) Without tentacle-like processes 13 



13 (34) Body round, or ovate, or elongate in outhne, symmetrical. . . 14 



14 (15) Cilia of body confined to two (rarely one) many-rowed crowns or 



circles. Body thimble-shaped, with broad end forward, from 

 the flattened center of which rises an elevation bearing the 



mouth at the apex Didiniiim Stein. 



Representative species Didinium nasutum Miiller 1786. 



Body oval, broadly rounded posteriorly. One wreath of cilia near the 

 base of the proboscis, the other posterior to the middle of the body. 

 Nucleus band-like. Contractile vacuole posterior. Length 100 to 175 m- 

 Among decaying vegetation. 



Fig 462. Didinium nasutum. t:, contractile vacuole. X 95. (.\fter Blochmann.) 



15 (14) Cilia not limited to two crowns or circles i6 



16 (27) With pharynx absent or slightly developed 17 



17 (22) Anterior end rounded, not oblique 18 



18 (21) Without a terminal bristle 19 



19 (20) Ellipsoidal to ovate, rounded at both ends. Mouth anterior, leading 



into a short pharynx. Uniform ciliation. 



Holophrya Ehrenberg, 

 Representative species Holophrya sp. 



Species not determined. 



Fig. 463. Tlolophrya sp. X 300. (After Conn.) 



20 (19) Elongated, cylindrical, narrow in front, mouth terminal or subter- 



minal. No pharynx. Cilia longer at the anterior end. 



Nucleus divided into small pieces. . . C//«n/z'fl Quenncrstedt. 



Representative species Chaenia teres Dujardin 1841. 



Forms observed from the fresh waters of Connecticut are 

 ^■^■^ provisionally placed here. 



Fig. 464. Chaenia teres. X 350. (After Conn.) 



