64 Annals of the South African Museum. 



a species recorded from the East Indies, Japan, and the Samoa 

 Islands. There is a Cancer ursus, Fabricius, but that does not pre- 

 occupy the use of the specific name in the clearly different genus 

 Cancer (Astacus). Herbst's third species, ursus minor, instead of 

 being a variety of ursus major, is accepted as a synonym of ScyUanix 

 arctus. Lund's remaining species, aequinoctialis, is the type of 

 Scyllarides, Gill. Hence each of the four species which Lund 

 acutely distinguished stands now under a separate generic name, 

 Scyllarus, Scyllarides, Parribacus, Tlienus. Balss in his important 

 treatise on East-Asiatic Decapoda (Abhandl. K. Bayer. Ak. 

 Wiss., vol. 10, Suppl. 2, p. 81, 1914) states that " Paribaccus 

 papyraceus Eathbun 1906," is a synonym of "Paribaccus antarc- 

 ticus (Humph.)," in his spelling of the generic name being no 

 doubt misled by Bate's change of Ibacus into Ibaccus, which he also 

 adopts, without noticing that the authors whom he cites usually 

 follow Leach and Dana, though Parribacus is sometimes changed to 

 Paribacus. 



GEN. THENUS, Leach. 



1815. Tlienus, Leach, Trans. Linn. Soc. London, vol. 11, p. 338. 



1816. ,, Leach, Encycl. Britannica, ed. 5, Supplement, 



pp. 417, 419, Art. Annulosa. 



1825. Scyllarus (part), Desmarest, Consid. gen. Crustace's, p. 181. 



1837. Themis, Milne Edwards, Hist. Nat. Crust., vol. 2, p. 285. 



1841. ,, de Haan, Crust. Japonica, decas 5, p. 151. 



1852. ,, Dana, U.S. Expl. Exp., vol. 13, p. 516. 



1888. Bate, Rep. Voy. Challenger, vol. 24, pp. 56, 65. 



1891. Ortmann, Zool. Jahrb., vol. 6, p. 38. 



1893. ,, Stebbing, Hist. Crust., Internat. Sci. Ser., vol. 74, 



p. 193. 



In his Zoological Miscellany, vol. 2, p. 152, 1815, Leach 

 remarks that "Ibacus is one of four distinct genera that have 

 been confounded under the general appellation Scyllarus." 

 He presently instituted the genus Tlienus, to which Dana 

 added Parribacus in 1852. The characters given by Leach 

 for distinguishing Tlienus from Scyllarus were, " Hinder legs 

 with simple tarsi. Thorax subdepressed, broader anteriorly. 

 Eyes inserted at the anterior angles of the thorax." The last 

 character is emphasized by Herbst in his description of the type 

 species by the remark that " in no single known insect do the 

 eyes stand so far apart." Ortmann uses this character and 

 the non-chelate fifth peraeopods of the female to distinguish 



