ii8 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL.97 



II III+IV 



Fig. 50. — Cephalic structures of Crustacea in which the protocephalon (acron 

 and first somite) is either the definitive head, or is united with several follow- 

 ing somites to form a more extensive syncephalon. 



A, Eubranchipus vernalis Hay (Anostraca) : protocephalon a distinct head 

 lobe (Prtc) separate from mandibular somite (II) ; maxillary somites (///, 

 IV) united with each other. B, Apus longicandatus Le Conte (Notostraca), 

 dorsal view : mandibular and maxillary somites united with protocephalon, maxil- 

 lary tergum produced in large cephalic carapace (C/>). C, same, ventral view 

 of head, showing labrum, antennules, mandibles, and maxillae. D, Daphnia 

 p-iilex Degeer (Cladocera) : head structure as in Apus, body covered by bi- 

 valved maxillary carapace. E, Eubranchipus vernalis, detached mandibular seg- 

 ment, anterior view, showing mandibles suspended from tergum, and mandibu- 

 lar musculature. F, Ncbalia bipcs Fabr. (Leptostraca) : bivalved carapace has 

 same composition as in Apus and Daphnia. G, section of head of Ncbalia show- 

 ing muscle attachments of protocephalic appendages. H, mandibles of Nebalia, 



