66 TWELFTH ANNUAL REPOKT. 



very similar to D. pules, it may be recognized at once by the con- 

 cavity of the dorsal margin of the post-abdomen. The plate will 

 make any detailed description superfluous. A common species in 

 Europe, but not yet found in America. 



Daphnia ovata, Sars, seems probably this species, but Sars was 

 troubled by Straus' mistaken reference. 



Daphnia pennata of Sars may al'-o be this species or, more prob- 

 ably, D. pulex. The Latin discription given by Sars is appended 

 for convenience of reference. 



Daphnia pennata, Sars. 



"Autecedenti (D. pulex) simillima, caput autem a latere visum latius, rostro breviore, 

 supra visum testa cetera pirum angustms fere cordiforme, autice acuminatum. Pro- 

 cessus aateriores duo disjunct!. Margo posterior postabdominis in medio sinulo parvo 

 et infra hunc utrinque aculeis 16-18 armatus. Color ut in autecedente. Longit.2Mmm.'" 



Daplinia ovata, Sars. 



"Caput a latere visum ante oculum fere angulatum,margine inferiore leviter concave 

 in rostrum longum apicem versus attenuatum, exiremitate tenuissima exeunte, spura 

 visum ut in D. pennata cordiforme. Testa cetera a latere visa ovata, margine superi- 

 ore et inferiore in femina adulta fere jequres arcuatis, postiee in medio spinam formans 

 brevissimam vel omnino obsoletam. Processus anteriores duo abdominis disjuncti- 

 Margo posterior postabdiiminis in medio sinuatus, utrinque aculeis 20-22 armatus. Color 

 albido— flavescens vel-viresceus. Longit. circit 3 mm." 



Sp. 3. Daphnia pulex, Mueller 



This commonest of our Daphnids is apparently circumpolar in 

 distribution. I have found it in Alabama near the Gulf and it also 

 occurs near lake Superior. 



Oval, either elongate or short, spine springing from the upper 

 angle of shell or in some cases near the middle. The spine is rather 

 long in young individuals but becomes very narrow in older ones 

 or entirely disappears. The abdominal processes are long, not 

 coalescent, or slightly united at the base. The head is concave be- 

 low and extends into a prominent beak. This species is either very 

 variable or several species are frequently united under the 

 term. Two types have been recognized in America. One, abun- 

 dant in spring in smaller ponds in Minnesota, is rather short, 

 arched above, and in old females with the spine situated near the 

 middle of the posterior margin. This form is quite typical for the 

 species and occurs from April to inid-summer. Another variety was 

 found in Alabama in late autumn, and similar animals in mid- winter 

 in lake Calhoun, Minnesota. This type has a much more elongate 

 bod}', the very slender but rather short spine springs from the upper 



