TN Ve eT AD te = 
264 GEOL. AND NAT. HIST. SURVEY OF MINNESOTA. 
Chydorus letourneuxi Richard. 
Richard ’88. 
Testa a latera visa subrotundata, sulcis curvatis (10-12) e medio exeuntibus, ad 
margines anticos liberos porrectis, antice manifestis ut in Plewroxus adunco, ornato; 
testis cetera levis, margine superiore prominente, postice leviter sinuato, marginalibus 
posterioribus et inferioribus rotundatis. Valoulorum margines inferiores postice 
ciliis longis instructi, margines superiores dentati. Rostrum breve et obtusum. 
Antenne 1 mi paris ad basin crass, rostro breviores, setis eequalibus. Antennz 2 
di paris setis 7 preeditee. Macula nigra oculo duplo minor, inter oculum et apicem 
rostri fere in medio sita. Postabdomen apicem versus rotundatum, unguibus termi- 
nalibus brevibus levibus ac robustis, aculeis ad basin 2, quorum interior altero 
multo brevior, armatis; margo superior in medio sinuatus supra medium processum 
obtusum format et infra hune aculeis minutis dense obsitus. Spinulis mintutissi- 
mis sparsim in lateribus post-abdomen instructum. Color corneus. Longit. circit 
0.5 mm. Mas ignotus. Algeria and Tunis. 
Chydorus alexandrowii and C. tuberculatus ef Poggenpol are confess- 
edly imperfectly described. We incline to the belief that there are 
not more than four good species in this genus, but extended study of 
the conditions of variation are necessary. 
GENUS ANCHISTROPUS Sars. (7?) 
Very similar in form to Chydorus; valves gaping below anteriorly; 
antennules small; process of labrum rounded. Post-abdomen atten- 
uated toward the end, densely covered with fine teeth; terminal claws 
denticulate. First foot with a powerful claw, protruding beyond the 
shell. Eye very large. Shell indistinctly reticulate. Sars says of 
his Anchistropus emarginatus that on cursory inspection it would be 
taken for the young of Chydorus globosus. He found but few speci- 
mens, about 0.35 mm. long. The suggestion is still possible that the 
young males of some Chydorus are here mistaken for a new genus. 
The males of Chydorus globosus were not known till 1878, and their 
early form is still unknown. The young females have a tolerably 
strong claw, though it is not much curved. I once found a 
peculiar Iynceid measuring 6.46 mm., with unevenly but distinctly 
reticulate shell, slender abdomen, and a strong claw. which was 
dentate. There were several young (more than two), and the shell in 
these was more regularly reticulate. All efforts to find a second 
specimen failed, and the one seen was somewhat mutilated; hence I 
am unable to determine its real position. 
GENUS MONOSPILUS Sars. 
Head separated by a depression from the body; shell high, com- 
pressed, posterior margin somewhat less than the greatest height of 
the shell. Post-abdomen broad, ornamented with lateral and posterior 
