700 FRESH-WATER BIOLOGY 



48 (24) No rostrum. Cervical sinus present. . . . 



49 



49 (65) Head small and depressed. Antennules small. Valves oval or 

 round. No post-anal extension of post-abdomen. 



Ceriodaphnia Dana 1853 . . 50 



General form rounded or oval; size small, rarely exceeding i mm. Vertex a rounded or angu- 

 lar projection, usually nearly filled by eye. Valves oval or round to subquadrate, usually 

 ending in a sharp dorsal angle or short spine. Antennules not very freely movable. One 

 abdominal process ordinarily developed. Post-abdomen of various forms, large. Ephippium 

 triangular, with one egg placed longitudinally. Antennules of ^ with long, stout seta, modi- 

 fication of flagellum; first foot with hook and long flagellum. Free swimming; motion 

 saltatory. 



50 (51) Head with a short spine or horn. 



Ceriodaphnia rigaudi Richard 1894. 



Valves reticulated. Head produced in front of antennules into a 

 short, conical, sharp-pointed, hornlike process. Two abdominal proc- 

 esses. Post-abdomen with 5-6 anal spines. Claws smooth or den- 

 ticulate. Antennules rather slender; lateral sense-hair somewhat 

 distal to middle. Length of 9> 0.4-0.5 mm.; d (South American), 

 0.38 mm. 



Pools; Louisiana, Texas. 



The form with horn on vertex also is found in South America, 

 mingled with typical C. rigaudi. Probably both forms should be in- 

 cluded in C. cornuta Sars. 



Fig. 1078. Ceriodaphnia rigaudi. 



51 (50) Head without horn 52 



52 (53) Claws pectinate Ceriodaphnia reticulata (Jurine) 1820. 



Head obtusely, or not at all, angu- 

 lated in front of antennules. Valves 

 reticulated, ending in spine or angle. 

 Antennules small, with sense-hair near 

 apex. Anal spines 7-10. Claws with 

 pecten of 6-10 teeth and denticulate. 

 Color variable, shades of red and yel- 

 low. Length of 9. 0.6-1.4 mm.; of 

 $ , 0.4-0.8 mm. 



Common, widely distributed. 



Fig. 1079. 



Ceriodaphnia reticulata, with 

 ephippium. 



53 (52) Claws not pectinate 54 



