28 Grust. 
CRUSTACEA. 
Lepidurus couesi (Packard, 1876), Montana, 49® N., and hilobatus, sp. n., 
Colorado, Packard, Bull. U. S. Geol. Surv. iii. pp. 177-179, with wood- 
cuts.* 
Estheria calif ornica (Packard) fully described by H. Lenz, Arch. f. Nat. 
xliii. pp. 24-40, pis. iii. & iv. 
OLADOOEIIA. 
A. Gerstacker gives an analytical table of the 31 known genera, 
arranging them in 6 families : — Podontidcc (including Evadne), Polyphe- 
midoSj Leptodoridce^ LynceidcCj DapJinidce^ and Sididce^ the three former 
forming the subtribe Gymnomera (Sars), the three latter the subtribe 
Calyptomera (Sars), and adds numerous general remarks on their 
biology and geographical distribution. Klass. u. Ordn. d. Thiorreichs, 
Arthropoden, pp. 1030-1033, 1038, 1041-1043, 1046, 1050, 1061, 
1063-1065. 
A. Weismann has published an elaborate paper on the formation of 
winter-eggs in all families, and many genera, of Cladocera ; the general 
result is, that in all of them a group of four cells is needed for an egg, 
three of which yield nourishment to the fourth (generally the third with 
regard to situation in the germinal stratum), which is transformed 
directly into an egg ; the summer-eggs are nourished by the fluid in 
which they float ; winter-eggs are formed also without fecundation, but 
without it do not come to perfection and are again dissolved, either in 
the ovary or later in the ephippium. Z. wiss. Zool. xxviii. pp. 93-254, 
pis. vii.-xi. 
The same author states that with regard to the alternation of sexual 
and non-sexual generations, the Daphnoidea [^Cladocera'] exhibit the fol- 
lowing differences : — 
(1) Those which live in the midst of great lakes or in the sea, have 
only one sexual period in the year, before the beginning of frost ; the 
eggs produced by sexual fecundation securing the preservation of the 
species during winter. Leptodora^ Bythotrephes^ Daphnia hyalina^ Sida, 
Latona, Daphnella hrachyura. 
(2) Those which live in ponds have two or three sexual periods in the 
year, as not only the winter, but also exsiccation in the warmest part of 
the summer, may interrupt the asexual propagation. Daphnia pulex. 
(3) Those which live in shallow pools and puddles easily subject to 
exsiccation, have an indefinite number of sexual periods in the year, 
males making their appearance as early as the second generation of 
the year, and both sorts of propagation being found at the same time. 
Moina. 
(4) In Bosmina longirostris and Pleuroxus trigonelluSy living in large 
lakes, no sexual period has hitherto been observed ; they are perhaps only 
propagated asexually. 
Polyphemus oculus has only two sexual periods in the first half of the 
summer ; in August no living animals are tp be found, but only eggs 
destined for the next year. Ber. Vers. Naturf. Munich, 1877, p. 178. 
