10 



is prolonged into a rather sharp beak, at whose apex the continu- 

 ations of the fornices unite. The beak does not project down- 

 ward, as in S. mucrona r a, but backward, and in its natural posi- 

 tion lies between the valves. The valves closely resemble in 

 shape those of S. mucronata. The shell of the head is reticu- 

 lated, as is also that of the area a (Plate I, Fig. 9). The area b 

 has a few strong striae and a few cross markings connecting these. 

 There are only one or two striae parallel to the lower edge of the 

 shell, and occasionally, in large specimens, two or three parallel 

 to the hinder edge. The rest of the valves bear numerous small 

 pointed projections. The " mucro " is short and blunt. The an- 

 tennules are much larger than in S. mucronata, though they do 

 not project beyond the rostrum. They have a flagellum and a 

 cluster of knobbed sense hairs, and are freely movable. The 

 rami of the antennae are never opaque. The macula nigra is long 

 and large, and somewhat resembles that of Simocephalus vetulus. 

 The post-abdomen has the same general shape as that of the pre- 

 ceding species, but is not opaque. The terminal claws have sev- 

 eral fine teeth on their outer sides. 



The male has the continuation of the fornices prolonged into a 

 rounded projection on each side of the rostrum. These protect 

 the large curved antennules, which are abundantly provided with 

 sense-hairs. The vas deferens opens close behind the terminal 

 claws. 



Color greenish white, varying to opaque, but usually quite 

 transparent. 



In antennules and macula nigra this species resembles Simo- 

 cephalus much more closely thafi. does the preceding species. 

 Embryos very closely resemble those of Simocephalus. 



GENUS 5. 

 Daphnia. Schodler, 1858. 



Daphnia, Schodler. Branch, der Umg. von Berlin, p. 10. 

 11 Sars, P. E. Miiller, Kurz. 



" and Hyalodaphnia, Schodler. Cladoceren des frischen Haffg, 

 p. 16. 



Daphnia, as thus limited, forms a very natural group. It con- 



