36 TAVELFTH ANNUAL RErORT. 



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

 the specimens which may be obtained in America. There seems, 

 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. inegops, Sars. 



2. C. cristata, Birge. 



B. 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. alahamensis, Herrick, (autennules elongate.) 



b. Shell siniply marked. 



(cc) Claws with teeth. 



6. C reticulata, Jurine. 

 [7]. C. dentata, Birge. 



(dd) Claws without teeth. 



I. Antennse very long. 



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



II. Antennae 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. 



tt Head abruptly angled behind the eye. 



12. C. scilula, Herrick. 



C. Shell reticulate with rectangular meshes. 



13. C. nilida, Schoedler. 

 [14]. C. lextilis, Dana. 



Sp. 1. Ceriodaphuia megop.s, Sars. 

 (Plate A. Figs. 16, 20.) 



Cerioiaphnia megops, Sars, P. E. MuKLLEB, KuRz. (The earlier synonymy is]donbtfu> 

 See note, page 26, Schoedler's Neue Beitrage zurNaturgeschicht& 

 der Cladoceren, 



