736 FRESH-WATER BIOLOGY 



237 (236) Denticles of ordinary size; infero-posteal tooth present. . . 238 



238 (243) Claws with one basal spine 239 



239 (242) Rostrum long, recurved 240 



240 (241) Shape elongated oval; valves striated 



0.1 MM 



Fig. 1 162. Alonella rostrata. 



Alonella rostrata (Koch) 1841. 



General form not unlike a Pletiroxus of the striatus 

 type. Valves striated or reticulated; infero-posteal 

 angle rounded and with minute tooth, sometimes ab- 

 sent. Rostrum long, slender, recurved. Post-ab- 

 domen moderately long, somewhat tapering toward 

 apex; angle rounded; 9-12 small marginal denticles. 

 Claws with i minute basal spine. Color yellow or 

 brown, usually rather dark. Length, 9' ca. 0.5 mm.; 

 $ , ca. 0.4 mm. 



Rather rare; reported from New England, Michi- 

 gan, Wisconsin, Minnesota; probably to be found in 

 all regions. 



This species is Pleuroxus acutirostris Birge. 



241 (240) Shape short oval; 



0.1 MM. 



valves strongly reticulated. 



Alonella dadayi Birge 1910. 



Shape oval-rotund. Valves strongly reticulated 

 all over; infero-posteal angle rounded, with sev- 

 eral minute teeth. Rostrum long, pointed, re- 

 curved. Keel of labrum acuminate behind and 

 its margin with i projection. Post-abdomen 

 short, wide; pre-anal angle strongly marked, as 

 in Chydorus; with numerous small denticles; apex 

 rounded. Claws with i basal spine. Color 

 yellow to brown, often opaque. Length, 9i 

 0.25-0.3 mm.; $ (South America), 0.2 mm. 



Louisiana, Texas; not rare in weedy pools. 



This species is Leptorhynchus dentifer Daday, 

 whose specific name has to be changed on remov- 

 ing to Alonella, as Sars' species A. dentifera pre- 

 occupies the name. 



Fig. II 63. Alonella dadayi. 



242 (239) Rostrum short or moderate; shape globose; valves conspicuously 

 striated Alonella nana (Baird) 1850. 



Very minute; Chydorus-like. Valves coarsely and con- 

 spicuously striated; minute tooth in infero-posteal region. 

 Rostrum varies, usually rather long, recurved, consider- 

 ably exceeding antennules. Post-abdomen short; pre- 

 anal angle strongly projecting; apex rounded; about 6 

 marginal denticles. Claws with i small spine. Color 

 brownish, usually opaque. Length, 9» 0.2-0.28 mm.; 

 $ , 0.25 mm. 



New England, Wisconsin, Minnesota; rare. The small- 

 est member of the family. 



Fig. 1164. Alonella nana. 



OJ MM. 



