36 TAVELFTH ANNUAL REPORT. 



The following artificial key, it is believed, will assist in placing^ 

 the specimens which may be obtained in America. There seem& 

 no reason to doubt that our fauna is very similar to that of north 

 Europe. Of the twelve species here enumerated at least one-third 

 may be synomyms and others of the remainder are with difficulty 

 distinguished. 



Artificial Key to the Genus Ceriodaphnia. 

 A. Shell irregularly striate. 



1. C. tnegops, Sai'S. 



2. C. crisiata, Blrge. 



Shell with hexagonal meshes. 



a. Shell with doubly contoured markings. 



(aa) Head broad, short. 

 8. C. pulchella, Sars. 

 (bb) Head narrowed, depressed. 



4. C. rotunda, Straus, (antennules normal.) 



5. C. ataftamensis, Herrick, (antennules elongate.) 



b. Shell simply marked. 



(cc) Claws witli teeth. 



6. C. reticulata, Jurine. 

 [7]. C. dentata, Birge. 



(dd) Claws without teeth. 



I. Antennoe very long. 



8. C. punctata, P. E. Mueller. 



II. Antennte normal or short. 

 * Post-abdomen broad. 



9. C. laticaudatus, P. E. Mueller. 1 mm. long. 

 [lOJ. C consors, Birge. 0.5 mm. long. 



** Post-abdomen narrow. 



t Head not angled behind the eye. 



11. C. quadrangula, Mueller. 



+t Head abruptly angled behind the eye. 



12. C. scitula, Herriek. 



C. Shell reticulate with rectangular meshes. 



13. C. nitida, Schoedler. 

 [14]. C. texlilis, Dana. 



Sp. 1. Ceriodaphuia meg^ops, Sars. 

 (Plate A. Figs. 16, 20.) 



Cerioiaphnia megops, SARS, P. E. Mueller, Kurz. (The earlier synonymy;isidoubtful 

 See note, page 26, Schoedler's Neue Beitrage zur Naturgeschichte 

 der Cladoceren. 



