218 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
GENUS ACANTHOLEBERIS Lilljeborg. 
Body more or less quadrangular, head triangular, acute cephalad, 
bearing the antennules at the front. Fornix slightly developed. 
Head scarcely separated by a depression from the body. Antennules 
elongate, expanded apically. The three-jointed branch of the antenne 
has five setze, the four jointed ramus has three, all being apical. The 
seta of the basal joint of the three jointed ramus is elongate. Labrum 
with an acute process. Feet six pairs. Intestine with a loop. Post- 
abdomen broad, armed with a series of spines. Margin of the shell 
with long spines below. 
Ancantholeberis curvirostris O. F. Miiller. 
PLATE XLVI, Fias. 1-4. 
O. F. Miiller 1785 (Daphnia curvirostris); Schoedler ’46 (Acanthocercus rigidus); 
Lievin 748 (Acanthocercus rigidus); Lilljeborg 52, and ’&8 (1igida); Leydig ’60 
(rigidus); Norman ’63; Norman and Brady ’67; P. E. Mueller ’68; Lund ’70-’71; 
Hellich °77. 
This rare species has not yet been found in America but may be 
confidently expected. The aspect is macrothroid, the whole ventral 
margin being long ciliate, while from near the posterior angle arise a 
number of greatly elongated sete. The caudal margins are armed 
with short spines. The macula is present but rather small. The an- 
tennules are elongate, expanded toward the tip, somewhat curved and 
armed apically with about eight unequal lanceolate processes and 
swwaller spinules. The post-abdomen is broad, rounded distally. The 
claws have two small basal teeth and a series of small sete. The pos- 
terior margin is armed with a series of small teeth. Length less than 
1.5 mm. 
GENUS OFRYOXUS Sars. 
Lyncodaphnia—Herrick. 
Body elongated, somewhat rectangular as seen from the side, great- 
est width and height of shell a little posterior to the heart; head sepa- 
rated by a depression from the body, truncate below; antenne and 
antennules much as in Macrothrix; four jointed ramus of antennee with 
no lateral setze; eye small, pigment fleck present; intestine twice con- 
voluted, expanded posteriorly, with anterior but no posterior ceca, 
opening near the ‘“‘heel’’ of the post-abdomen; post-abdomen large, 
triangular; terminal claws long, rather straight, with two accessory 
spines at the base. 
Ofryoxus is, aS Was suggested, a curious transition form linking the 
Daphnide with the Lynceide. 
