ANNULOSA. 555 



The following is the arrangement employed by Dr 

 Leach : 



Division I. Body covered by a horizontal shield. Eyes 

 sessile. 



Subdivision I. Shield composed of two distinct parts. 



1. LlMULUS. 



Subdivision 2. Shield composed of but one part. 



* With jaws. 



2. Apus. 



** With a rostrum, but no jaws. 



a. Antennae four. 



S. Argulus. 



h. Antennae two. 



4. Cecrops. 5. Caligus. 6. Pandarus. 7. An- 



THOSOMA. 



Division II. Body covered by a bivalve shell. Eyes 

 sessile. 

 S^d)division 1. Head porrected. 

 8. Lyxceus. 9. Chydorus. 10. Daphnia. 

 Subdivision 2. Head concealed. 



11. CyPRIS. 12. CVTHERE. 



Division III. Body covered neither by a bivalve shell 

 6r shield. Eye one, sessile. 



13. Cyclops. 14. Calanus. 15. Polyphemus (Di- 

 chelesfmm). 



Division IV. Body covered by neither a bivalve shell or 

 shield. Eyes pedunculated. 



16. Branchiopoda. (17. Artemia. 18. Eulimene). 



There are two tribes of animals which have so many re- 

 lations to the Crustacea, in form at least, and partly in 

 structure, that wc have ventured to take some notice of 

 them here. 



