EN^TOMOSTRAOA OF MINNESOTA. 213 



mm. high, while the present form measures 1.1 by 0.7 mm.) but the 

 form and several details noticeably differ. The shell, as seen from the 

 side, is nearly quadrangular, reminding of Lathonura, and is not 

 produced into a sharp spine as in 21. rosea. The head is also shorter 

 and is not excavated between the eye and pigment fleck. The ventral 

 margin of the valves is not obviously sinuous and is spinulus as in 3L 

 rosea. The antennules are straight, and not strongly curved, as fig- 

 ured by Kurz, neither are they spiny in front. At the tip they bear 

 the usual sensory setse and posteriorly a cluster of spines while the 

 posterior margin is ornamented with several clusters of bristles dis- 

 tally. The antennae seem not to differ materially from those of 31. 

 rosea. The post abdomen is shorter than in M. rosea, its terminal 

 claws are small, curved, deep-colored and unarmed; in the protuber- 

 ance formed by the anus are closely clustered spines and bristles 

 while the rest of the margin is either unarmed or furnished with a 

 few minute spines. The long stylets are as usual in the genus. No 

 markings were seen on tlie shell. Projecting into the brood-cavity 

 are two leaf-like plates which seem to serve an accessory branchial 

 function and contain many blood corpuscles. Details of the feet are 

 wanting. The species has been but once seen, in the clear water of 

 the tank supplying Albuquerque, New Mexico, accompanied by two 

 species of Diaptomns and a 3Iouia. 



31. rosea occurs in the north, often in considerable numbers (Birge 

 '91) and the present species may take its place to the southward. It 

 may be admitted that it approaches Lathonura more than any other 

 species of the genus. 



It is just brought to my notice that Matile describes in an appendix 

 to his paper " Die Cladoceren der Umgebung von Moskau, 1891," 

 Macrothrix bori/sthenica, which is so very close to our species that we 

 suspect intimate comparison will prove the two identical. The atten- 

 nules in Matile's species are shorter and the dorsal margin is less 

 strongly marked. The armature of the post-abdomen is perhaps 

 slightly different but our description was drawn from very large in- 

 dividuals and considerable variation was observed. I therefore with- 

 draw the name proposed for the present. 



Macrothrix liirsuticornis Norman and Brady. 

 Norman and Brady '67; Daday '83; Matile '90. 



Head separated from the thorax by a depression. Shell roundish, 

 caudal angle obtuse, smooth, ventral margin gently rounded. An- 

 tennules dilated toward the end, slightly curved, cephalic margin with 

 £.ve series of small sette. Post-abdomen rounded at the end, having 

 <iistally seven sette and proximally small teeth. Length 0.55 mm. 



