336 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
GENUS DARWINULA Brady and Robertson. 1870. 
‘*Shell smooth, thin, and fragile. Carapace oblong, higher behind 
than in front; lucid spots ten to twelve in number, linear-oblong or 
wedge-shaped, arranged in a subradiate manner in front of the centre 
of the valve. Seen from the side, compressed, oblong, sub ovate. 
Seen from above, ovate, acuminate in front, obtusely rounded behind. 
Valves unequal, the right much larger than the left. Antennules 
very short, six-jointed, and stout, strongly armed with short and stout 
curved sete. Antenne four-jointed, and bearing four or five strong 
terminal claws; entirely destitute of poison gland or urticating sete, 
the place of which is occupied by a single curved seta of moderate 
length. Mandible broad, truncated at the distal extremity, which is 
provided with six or seven small spiniform teeth; palp three jointed, 
its basal joint very wide and fringed with several curved set, bearing 
also a small lamina, fringed with branchial filaments; second joint 
long, slender, and nearly four times as long as broad, slightly curved 
and dilated at the distal extremity, where it bears one long and two 
small setze; terminal joint more slender, about two-thirds of the length 
of the foregoing, and bearing at the truncate apex about six slender 
curved spines. First maxilla divided into four short setiferous seg- 
ments, and bearing a very long oblong palp, which is fringed with 
about twenty-four long branchial filaments, and has also four other 
long sete at its base. Second maxilla simple, short, and broad, trun- 
cate at the apex, and fringed on the distal margin with several slender 
spine-like hairs, bearing also a large, three jointed, pediform palp, and 
an ovate branchial appendage of moderate size. Two pairs of feet 
of moderate size, five-jointed; second pair much the longest, and hav- 
ing the last joint armed with one long and two small curved sete; 
first three joints of nearly equal length; fourth and fifth, respectively, 
about one-half and one third as long as the preceding. Abdomen 
ending in a short conical process. Copulative organs of the male of 
complex structure, the basal portion of an irregularly-shaped plate 
produced laterally into an aliform process, and on the distal margin 
into a short, strong hook. Female probably viviparous.” (Brady 
and Norman, 31.) 
Darwinula improvisa sp. n. 
PLATE LXXXI, Fi@s. 1-3, 13. 
Length of female 0.68 mm. Height 0.27 mm. Width 0.24 mm. 
Length of male 0.70 mm. Height 0.23 mm. 
The right valve is larger than the left and overlaps it on the ven- 
tral side. In the female the height is more than one-third of the 
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