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. 



Siniocephalus 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; ephippium large, triangular, with one egg. Antennules 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 vetulus (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 mm.; ^ , ca. 

 i.o mm. 



Not very abundant, but found every- 

 where in weedy water. 



Fig. 1073 • 



0.1 MM 



Simocephalus vetulus, with 

 ephippium. 



43 (42) Ocellus rhomboidal or round. Vertex with obtuse or rounded angle. 

 Claws pectinate. . . 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.omm.; ^, to 1.3 mm. 



Not common; reported from Massachu- 

 setts, Wisconsin, and the southern states. 



Fig. 1074. Simocephalus exspinosus. 



