:91 TWELFTH ANNUAL REPORT. 



6. A. modesta, Herriok. (Shell straight above.) 



** Post-abdomen not narrowed. 



+ Antennae with seven setae. 

 (?) 7. A . costata, Sars. 



ft Antennae with eight setae. 



8. A., quadrangularis, Mueller. 



IIL Shell faintly, irregularly striped; eye of same size as pigment fleck. 



9. A. oblonga, P. E. Mueller. 

 IV. Shell smooth. 



10. A. afflnis, Leydig, 



<b) Under 0.5 mm. in length. 



I. Post-abdomen armed with a row of hairs terminating in large teeth. 



11. A. dentata, P. E. Mueller. 



II. (One or) two rows of teeth present. 

 * Shell densely and evenly striate. 



12. A. elega7is, Kurz. 



** Shell not densely lined. 



t Shell smooth or lined longitudinally. 



t Teeth of post-abdomen unequal, the lower ones enlarged. 



13. A. porrecta, Blrge. 

 tt Teeth nearly equal. 



§ Form elongated ; abdomen with a lateral line of spiny scales. 



14. A. spinifera, Schoedler. 



§§ Form squarish ; abdomen with a lateral line of simple spines or bristles, or 

 neither. 



15. A. parvula, Kurz. 



16. A. glacialis, Birge. 



Xtt Clusters of bristles, not spines, on the posterior edge of the post-abdomen. 



17. A. intermedia, Sars. 



++ Shell smooth or tuberculate. 

 18, 19. A. tuberculata, Kurz, Herrlck. 



Sp. 1. Alona guttata, Sars. 



A small species ©f sub-quadrangular form. The beak is very short; 

 the eye small, but larger than the minute pigment fleck. The shell 

 is short, with a rounded posterior angle and marked by hexagonal 

 or rectangular meshes running about parallel with the lower margin. 

 The post-abdomen is of moderate size, rounded at the apex, with a 

 series of stout teeth behind; the terminal claw has a minute basal 

 spine. P. E. Mueller, in Danmark's Cladocera, confused this with 

 A. intermedia, which he described under this. The post-abdomen 

 in that species is larger, less rounded behind, and armed with 

 clusters of spines instead of teeth. The length is about 0.3 mm. 

 in both. 



