REPORT ON THE CRUSTACEA MACRURA. 57 



second, sub-chelate, the pollex never being produced beyond the length of the daetylos. 

 The three following pairs monodactyle or imperfectly chelate. The posterior pair is more 

 or less minutely chelate in the female, and monodactyle in the male. 



This tribe consists of genera that differ widely in their external aspect, but are closely 

 associated in structural affinities and development. Some are dorsally depressed, others 

 arc laterally compressed. Some have the ophthalmopoda projecting on an advanced 

 somite, others have them lodged in orbits excavated in the frontal margin of the carapace. 

 Some have the second pair of antennae long and slender, while others have them reduced 

 to a short discoid plate. 



But they all agree in the following points : — the character of the branchise, the 

 absence of a scaphocerite attached to the second pair of antennas, in having only six 

 joints to the pereiopoda, in having no true chela, in having the ova very small, and in 

 the Phyllosoma condition of the brephalos. The examination of an undescribed form 

 which I have named Synaxes, 1 in which several features of these two famibes are com- 

 bined, has induced me to arrange them all under one head. Synaxes has the antenna? 

 of Palinurus, while the pereiopoda are like those of Scyllarus, the carapace is like 

 that of Astacus, and the pleopoda like those of Scyllarus. Having no means of knowing 

 the character of the brephalos when it quits the ovum, and as both Palinurus and the 

 Scvllariform genera have the young hatched in the megalopa stage, resembling Phyllo- 

 soma, I am induced, until future observation demonstrates the fact, to believe that the 

 brephalos of Synaxes also resembles Phyllosoma. I therefore follow the arrangement of 

 previous authors and place the tribe under two families, into which it naturally divides, 

 Scyllaridas and Palinuridse. 



Family Scyllaeida 



Carapace horizontally depressed. Eyes implanted in orbits excavated in the dorsal 

 surface of the cephalon. Second pair of antenna? short, scmamiform. The mandibles 

 bearing a uniarticulate synaphipod. Pereiopoda simple, excepting the posterior pair of 

 the female which is minutely chelate. 



Tbaccus, Leach. 



Geographical Distribution. — Ibaccus incisus has been recorded from New Holland and 

 the adjacent seas; Ibaccus antarcticus from Japan and the coasts of Asia; and Ibaccus par rx 

 from the Antilles. Stimpson found Ibaccus novemdentatus at Hong Kong. De Haan 

 obtained Hxiccus ciliatus from Japan. Ibaccus brevipes was taken south of New Guinea; 

 Ibaccus alticrenatus off New Zealand, and Ibaccus verdi w r as taken in the Atlantic. 



No specimen of this genus, so far as I am aware, has ever been found fossil. 



1 Ann. and Mag. Nat. Hist., ser. 5, vol. vii. p. 220, pi. xiv. 

 (ZOOL. CHALL. EXP. — PART LII. — 1886.) Fff 8 



