168 AUSTRALIAN MALACOSTBACA. 



Passage (Queensland) ; unfortunately the abdomen has been 

 lost ; but it appears to be an undescribed species allied to C 

 longimana, Stimpson. 



Sub-Tribe Astacidea. 



Carapace often marked by a transverse dorsal (cervical) 

 suture ; the longitudinal sutures obsolete. Scaphocerite present, 

 well-developed or small, or obsolete. First pair of legs (cheli- 

 pedes) either didactyle or monodactyle. Branchiae penicillate. 



Family SCYLLARID^. 



Carapace much depressed, the lateral margins rather thin, 

 carapace suddenly inflexed laterally. External antennae laminate, 

 short, without a basal scale or scaphocerite. Sternum trigonous. 

 Anterior legs monodactyle. 



Genus Ibacus, Leach. 



Carapace transverse, the sides incised. Rostrum bilobate. 

 Eyes far removed from the external angles. External antenna; 

 not far removed from one another. Branchiae 21. 



316. Ibacus Peronii. A.M. 



Ibacus Peronii, Leach. Zool. Misc., t. ii., pi. 119 ; Desmarest, 

 Consid., p. 183, pi. xxxi., fig. 2 ; Milne-Edwards, Hist. Nat. 

 Crust, t. ii., p. 287. 



Orbits situated much nearer the middle line than the external 

 angles of the carapace, which are recurved in front and extend 

 further forward than the front. Carapace much depressed, 

 granulated, and presenting three longitudinal crests, of which 

 the median is ornamented with a few smooth tubercles, and the 

 lateral are situated on the same longitudinal line as the orbits ; 

 lateral borders of the carapace very oblique and armed with 

 seven teeth, of which only one is situated in front of the great 

 lateral incision, and forms the anterior angle. External antenna? 

 much broader than long, their first joint very small and scarcely 

 extending beyond the rostrum, the second feebly toothed, and 

 the fourth armed only with three or four very broad and not 

 very prominent teeth. External maxillipedes armed with spines 



