212 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 



*Macrotlirix laticornis Jurine. 



Plates LIV, Figs, 9-12; LVI, Figs. 8, 9. 



Jariae '20; Baird '50; Fischer '52 (Daphnia curvirostris); Lilljeborg '53; Schoedler 

 '58; Leydig '60; Norman and Brady '67; P. E. Mueller '68; Lund '70-'71; Fric 

 '721; Karz jj^. Hsrri^k '84; Birge '91. 



This iibicjuitous species was first reported in America by Birge 

 though it had been encountered by the writer in several instances. 

 It is recorded at Madison, Wis., Minneapolis, Minn., where it is not 

 rare, and in Albuquercjue, ]^ew Mexico. 



The body is compactly oval, with a curved or subangular lower 

 margin which is armed with spines which project in three planes, thus 

 producing three series; dorsal margin convexly arched, crenulate or 

 subdentate. Head short, produced veutro-cephalad to form a blunt 

 beak from which the antennules are suspended. Eye of moderate size; 

 pigment fleck large; quadrate. Antennules short, greatly expanded 

 at the tip, provided with the usual sensory set?e and flagella and a 

 cluster of spines at their bases, also a second cluster upon a special 

 protuberance posteriorly. Upon tlie anterior margin are series of 

 bristles and this margin is serrate. The antennae are strong, hairy, 

 and armed as usual in the genus. The feet are sufficiently represented 

 in the figures. The post-abdomen is short, with very small terminal 

 claws, in front of which are several bristles not previously noticed; 

 about the anus are several bristles, and a series of short teeth orna- 

 ments the dorsal margin. The whole shell is hexagonally reticulate 

 except along the dorson where the slight crest modifies the markings. 

 Length 4.7 to G.O mm. Birge found this form only rarely and then 

 singly. Fric speaks of it as loving the bottom and occurring singly. 

 We have frequently found it in Minneapolis and abundantly in New 

 Mexico, 



As the type of the genus, it appropriately occupies a conservative 

 position, as shown by broad tip of the antennules, a feature exhibited 

 by embryos and young of other species. 



* Macro tlirix nova-niexicana sp. n. 



Plate LIX, Figs. 3-5. 



Testa corporis suboblongata, levis, postice non angulata, marginalibus ventralibos 

 cequaliter rotundatus fere rectus, ciiiatas gerentibus. Oculus magnus; macula cere- 

 bralis parva sed manifesta. Antenna; fere rectse, ad apicem versus paulum dilatalse, 

 posticaj ciliatffi. Antennse 2 di paris ilia; M. rosea similes. Cauda brevis, apice 

 rotundato, super anum sinuata, ad apicem versus densa ciliata, margine cetero seribus 

 setarnm minimarum armato sive inermis. Longit 1.1 mm. 



As compared with M. rosea, its nearest ally, this form is not only 

 considerably larger (the largest figures being 0.9 mm. in length by 0.6 



