516 



CRUSTACEA. 



Fam. IV. Astacid^e. — Carapax oblongus, subcylindricus, abdomine 

 parce angustiore. Sternum angustum. 



In the first three families, the epistome is soldered to the inflexed 

 carapax either side, nearly as in the Brachyura ; in the last, this 

 union takes place by a suture and is less perfect, the edge of the cara- 

 pax being a little projecting. 



Family SCYLLARID^. 



The established genera of this family are Scyllarus, Ibacus, and 

 Thenus. The genus Scyllarus is subdivided into sections by Milne 

 Edwards ; and these sections of Scyllarus, as well as others of Ibacus, 

 are made into subgenera by De Haan, after a profound study of their 

 characters. De Haan has not named the new divisions; and in 

 adopting them as genera, we give names to those that are new. 



1. Carapax oblongus vel subquadratus, non transversus. Oculi versus cephalo- 

 thoracis angulos extemos insiti. 



G. 1. Scyllarus, Fabr. — Rostrum yalde saliens. Latera carapacis non incisa. 

 Antennae externae inter se fere contiguse. Palpus niaxillipedis externi flagello 

 confectus. Branchiae numero 21. Species, Be. sculptus, latus, squamosus, equi- 

 noxialis, Haanii, Sieboldi. 



Gr. 2. Arctus, Dana (Scyllari subgenus 5tum, De Haan). — Eostrum perbreve, 

 truncatum. Antennae externae inter se remotse. Palpus maxillipedis externi 

 flagello carens. Branchiae 19. Sp. A. ursus, J). (Scyllarus arctus, Auct). 



2. Carapax plus minusve transversus, laterihus non incisus. Oculi in angulis externis. 

 Gr. 3. Thenus, Leach. — Oculi oblongi. Rostrum bilobatum. Branchiae 21. 



3. Carapax plus minusve transversus, laterihus incisus. Oculi angulis externis valde 



remoti. 



G. 4. Parribacus, Dana (Scyllari subgenus 2dum, De Haan).— Rostrum sub- 



