STATE GEOLOGIST. 69 



31 acrothrix laticornis, BX1R.D, Ann. Ma,g. Nat. Hist. 



^icanthocercus currirostris {/), schoedler, Ericlis. Arcliiv, 1846. 



Dapfinia curvirostris, fischer. 



Mncrothrix laticornis, lillteborg, LErDiG, baird, p, e. muei.ler, fric, kurz, 

 SARS, LUTZ, CLAu.s (Die Sclialendruse d. Uaplinlen), norman 

 and BRADY (Monogr. Brit, lintom.), gruber and weismanx, 

 weismann, (Beitrage zur Natuvgeschiclite d. Dapb.) 



This is the commonest European species and is the type of the 

 genus, showing its rather conservative position by the broad tip of 

 the antenna which is a feature exhibited by embryos and young of 

 other species. The shell has a warty surface and is toothed above, 

 while the lower margins are fringed with long unequal spines in 

 groups of threes or fours. 



The form is roundish with a blunt posterior angle, the ventral 

 margin being regularly curved. The antennules are short and en- 

 larged at the end. The form is an irregular pentagon; a pair of 

 slender spines sits at the angle near the base. 



The swimming antennee with the seta on the first joint of 3- 

 jointed ramus very long. Post-abdomen truncate at the end, short, 

 posterior margin beset with series of bristles. 



Length of male 0.5 — 0.6 mm,, of female 0.4 mm. 



This is the smallest of the genus and will undoubtedly be found 

 in America. 



Sp. 2. Macrotlirix rcsea, Jurine. 



(Plate C. Fi^s. 5, 6, 11, and 13.) 



Monoculus roseus, jorine. 



Lunceus roseus, desmarest. 



Daphnia rosea, m. edwards, jurrell. 



Echinisca rosea, lievin. 



Macrothrix rosea, baird, ltlljeborg, p. e. mdeller, bibge. 



The body is sub-oval, terminating behind in an acute angle; the 

 lower margin is less conspicuously spined than the last or the 

 following; the antennae are but slightly dilated at the end and 

 nearly straight. The longest seta of the antennae is longer than 

 in the last, reaching beyond the tips of the terminal setae; abdo- 

 men more slender, sinuate in front, beset with short hairs. . 



Length 0.6 mm, male 0.3 mm. The male has no claws on the end 

 of the post-abdomen, and the antennules are curved and elongated. 

 Figures 5 and 13 are copied from Birge. 



