672 



FRESH-WATER BIOLOGY 



50 (51) Carapace short, three-fifths as long as exposed abdomen; telson with 



one (or two) median and two lateral spines on its dorsal 

 median third A pus lucasanus Fs-cksnd iSyi. 



An abundant and widely distributed species; reported from Lower Cali- 

 fornia and Kansas. 



Fig. 1035. Apus lucasanus. Telson. X 6. (After Packard.) 



51 (50) Carapace even shorter than in A. lucasanus; telson very short with 



one median and four lateral spines on dorsal median third. 

 Apus longicaudatus Leconte 1846. 



This form occurs in Colorado, Nebraska, Texas, and along the Yellowstone 

 River. 



Fig. 1036. Apus longicaudatus. Telson. X 6. (After Packard.) 



52 (37) Body compressed, carapace forming two lateral valves which enclose 



the body Suborder Conchostraca . , 53 



53 (60) Only the first post-cephalic Umbs prehensile in the male; carapace 



spheroidal, without Knes of growth; head not included 



within carapace-chamber Family Limnetidae. 



Only one genus Limnetis . . 54 



54 (57) Shell subspherical 55 



55 (56) Length, 3 mm.; front of male's head narrow; second antenna i6-seg- 



^ ^ mented; flabellum very large. . Limnetis gouldii Baird 1862. 



A form widely distributed through Massachusetts, Nevr 

 Hampshire, Rhode Island, New York, Illinois, and Canada. 

 It is very hardy and will live for months in aquaria. 



Fig. 1037. Limnetis gouldii. ^ , head of male, dorsal view. X 21; 

 B, shape of shell. X 7. (After Packard.) 



56 (55) Length, 4.2 mm.; front of male's head very broad; antenna 20-seg- 



mented Limnetis gracilicornis Packard 187 1. 



This species was described by Packard from specimens collected 

 at Waco, Texas. 



Fig. 1038. Limnetis gracilicornis. Head of male, dorsal view. X 18. 

 (After Packard.) 



57 (54) Shell suboval 58 



58 (59) Length, 4 nam.; front of male's head broad and square; second an- 



A B tenna 14- and 17-segmented; flabellum very narrow. 



Limnetis mucronatus Packard 1875. 



This species has been reported from Montana and Kansas. 

 It is easily recognized by the mucronate, tridentate front. 



^3 



Fig. 1039. Limnetis mucronatus. ^ , head of male, dorsal view. X 20; 

 B, shape of shell. X 4. (After Packard.) 



59 (58) Length, 4 (to 6) mm.; front of male's head rather broad; second 

 A B antenna 29-segmented; flabellum short and broad. 



Limnetis brevifrons Packard 1877. 



This is the largest known species of this genus in North 

 America. It has been observed only at Ellis, Kansas. 



Fig. 1040. Limnetis brevifrons. A, head of male. X 8. 

 of shell. X 3. (After Packard.) 



B, shape 



