29 



to the lower edge of the shell. They have JJ J setae and ^g J spines. 

 The last seta is, as usual, very much smaller than the others. The 

 macula nigra is much smaller than the eye, about one-third as 

 large in diameter. Two young are produced at once. A very 

 young specimen showed no striae. In the adult, these are about 

 0.025 mm. apart. 



The male is somewhat smaller than the female and of slightly 

 different proportions. It is 0.35 mm. long and 0.2 mm. high. 

 The rostrum projects farther forward and not so far down- 

 wards. The post-abdomen is rounded at the end, without teeth, 

 but with a row of fine hairs. The vas deferens opens below the 

 terminal claws. The body behind the heart rises up to the top 

 of the cavity of the valves. This position makes the abdomen 

 hang down nearly perpendicularly when at rest. The coils of the 

 intestine are larger than in the female, and the testicle lies imme- 

 diately on them. The front legs have the usual hook. The 

 cross markings of the sculpture are scarcely to be seen ; otherwise 

 it resembles the female. 



The reticulation of this species excludes it from all others of this 

 genus except A. guttata (Sars, Crust. Clad, i Omgn. of Christiania, 

 p. 287). In that species, however, the rostrum is shorter, the ma- 

 cula nigra much larger (" oculo parvo minor/' Miiller). the post- 

 abdomen "apice rotundato," and its teeth much smaller. The 

 general outline, too, is different, and the reticulation, instead of 

 running obliquely across the valves, is horizontal. It is also one- 

 fourth larger: 0.5 mm. instead of 0.4. A. reticulata (Schodler, 

 ISTeue Beitr., etc., p. 25), if not identical with A. guttata, is even 

 more unlike the present species. 



Cambridge, Mass., 1876. Not rare. 



SPECIES 2. 

 Plate I. Fig. 16. 



Alona Porrecta. sp. nov. 

 Length, 0.34 mm. Height, 0.19 mm. 



Anterior portion of valve with a sinus. Lower angle of post- 

 abdomen acute. Shell striated with horizontal lines. 



