698 



FRESH-WATER BIOLOGY 



39 (25) Cervical sinus present. No crest 40 



40 (45) Valves transversely striated. Post-abdomen broad, with indenta- 



tion in which anus opens. 



Simocephalus Schoedler 1858 . 41 



Body large and heavy; shell thick. Head and rostrum small. Valves large, somewhat 

 quadrate, with rounded angles and sometimes a posterior spine; marked with oblique striae, 

 anastomosing irregularly and with cross-connections. Two abdominal processes developed, 

 placed far apart. Post -abdomen large, broad, truncate, posterior end emarginate and bear- 

 ing the anal spines. Claws rather straight, always denticulate, sometimes pectinate. Summer 

 eggs numerous; epiiippium large, triangular, with one egg. Anteimules of $ like 9 but with 

 2 lateral sense-hairs. First foot without flagellum and with small hook. Poor swimmer; swims 

 often on its back. Color yellow to yellow brown. 



41 (44) Vertex rounded, smooth. No posterior spine on valves. . 42 



42 (43) Ocellus elongated. Vertex rounded over. Claws denticulate. 



Simocephalus veiulus (O. F. Miiller) 1776. 



Ocellus large, elongated, rarely rhom- 

 boidal. No spine on valves, though 

 there may be a blunt posterior angle. 

 Post-abdomen very broad, deeply 

 emarginate; anal spines about ten, de- 

 creasing from the claws; the larger 

 bent and ciliate at the base. Claws 

 long, slender, little curved, denticulate 

 only. Length, 9. to 3.0 rum.; $ , ca. 

 i.omm. 



Not very abimdant, but found every- 

 where in weedy water. 



0.1 MM. 



43 (42) Ocellus rhomboidal or round. 

 Claws pectinate. . . 



Fig. 1073. 



Simocephalus veluius, with 

 epbippium. 



Vertex with obtuse or rounded angle. 

 Simocephalus exspinosus (Koch) 1841. 



Valves much as in vetulus, but striae do not 

 anastomose so freely. Post-abdomen slightly 

 narrower toward apex; anal spines up to 12, 

 evenly curved, not bent; claws with pecten of 

 8-12 teeth and denticulate. Color and gen- 

 eral appearance much as preceding species. 

 Length, 9 . t03.o mm.; S , to 1.3 mm. 



Not common; reported from Massachu- 

 setts, Wisconsin, and the southern states. 



Fig. 1074. Simocephalus exspinosus. 



