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. 



I. LlMULJJS. 



Subdivision 2. Shield composed of but one part. 



* With jaws. 

 %. APUS. 



** With a rostrum, but no jaws. 



a. Antennae four. 

 8. ARGULUS. 



b. Antennae two. 



4. CECROPS. 5. CALIGUS. 6. PANDARUS. 7. AN- 

 THOSOMA. 



Division II. Body covered by a bivalve shell. Eyes 

 sessile. 

 Subdivision 1. Head porrected. 



5. LYKCEUS. 9. CHYDORUS. 10. DAPHNIA. 

 Subdivision 2. Head concealed. 



II. CYPRIS. 12. CYTHERE. 



Division III. Body covered neither by a bivalve shell 

 or shield. Eye one, sessile. 



13. CYCLOPS. 14. CALANUS. 15. POLYPHEMUS (Di, 

 chelestium). 



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 we have ventured to take some notice of 

 them here. 



