2206 CRUSTACEA. 



b. Caput breve. 



G. 6. Eurycerous, Baird* — Caput quoad rostrum paulo productum et infra 

 incurvatum. Antennae anticae rostro vix breviores. Abdomen perlatum. 



G-. 7. Lynceus, Muller.\ — Caput quoad rostrum valde productum et infra incur- 

 vatum, lateraliter visum tenuiter acutum (apice raro inflexum). Antennae anticae 

 minutae, prope rostri basin insitae et rostro plus dimidio breviores. Abdomen 

 latitudine mediocre. 



G-. 8. Alona, Baird.% — Caput quoad rostrum minus productum et paulo divari- 

 catum. Antennae anticae rostri apicem fere attingentes. Abdomen latitudine 

 mediocre. 



Fam. III. BOSMINIDiE. 



Pedes foliacei numero decern. Antennae anticae elongatae et multi- 

 articulatae. 



G. 1. Bosmina, Baird.%— Caput infra rostriforme, ad rostri apicem antennas 

 anticas gerens. Antennae posticae sat breves. 



Fam. IV. POLYPHEMIDiE.H 



Caput grande, oculis repletum. Pedes numero octo, fere teretes. An- 

 tennae anticae obsolescentes. 



G. 1. Polyphemus, Miiller.— Corpus apud thoracem posticum deflexum posteaque 

 quoad abdominem reflexum et tenue, extremitate setis duabus longis armata. 

 Caput discretum. Kamus antennarum posticarum unus 4 alter 3-articulatus. 



* This genus as adopted includes Ghydorus, Peracantha, and Pleuroxus of Baird 

 (Brit. Entomost.), which scarcely differ except in the form of the shell. 



f Baird, Brit. Entomost., 123. 



% Trans. Berw. Club, ii., Ann. and Mag. Nat. Hist., ii., Brit. Entomost., 131. We 

 include with Alona, the genera Acroperus and Camptocercus of Baird. The last is dis- 

 tinguished by having a very narrow elongated abdomen which is also flexible. In the 

 genus Alona, as adopted, the beak diverges from the body, and the inferior side makes a 

 large angle (between 60° and 90°), with the shell below or adjoining; while in Lynceus 

 the beak curves parallel with the shell, and makes a very small angle with it; other ana 

 better grounds for generic divisions may hereafter be detected. 



§ Trans. Berw. Nat. Club, 1845, Ann. Mag. N. H., xi. 412, Brit. Entomost., 105. 



|| Baird, Trans. Berw. Nat. Club., ii. 149, 1845., Brit. Entomost., Ill 



