2 CEYLON PEARL OYSTER REPORT. 



DESCRIPTION OF THE SPECIES. 



ISOPODA ANOMALA. 



" Tribe : CHELIFERA. 

 Family: TANAID.E. 



Tanais, Audouin and Milne-Edwards. 



1828, Tanais, Audouin and Milne-Edwards, 'Resume' d'Entomologie,' p. 182, pi. 29, fig. 1, and 

 'Precis d'Entomologie,' vol. 1, p. 46, pi. 29, fig. 1. 



The genus was named Anisocheirus by Westwood in 1832 ('Ann. Sci. Nat.,' 

 vol. 27), Zcu.ro by Templeton in 1836 ('Trans. Entom. Soc.,' vol. 2, p. 201), and 

 Crossurus by Rathke in 1843 ('Fauna Norwegens,' p 35). Sars, when defining it 

 in 1896 ('Crustacea of Norway,' vol. 2, part i., p. 11), remarked that it was well 

 distinguished from all the other genera of the family, especially by the circumstance 

 that the pleon was composed of only five segments and carried only three pairs of 

 pleopods. He assigned to it only four sjDecies : T. tomentosus, Kroyer ; T. cavolinii, 

 Milne-Edwards ; T. dulongii (Audouin) ; and T. novce-zealandice, Thomson. 

 According to Dollfus ('Bull. Soc. Zool. France,' vol. 21, p. 207, 1897) the first of 

 them is a synonym of the second. But several other species are on record, T. macro- 

 cheles, Nicolet, 1849; T. brasiliensis, Dana, 1849; T. loricatus, Bate, 1864; 

 T. gracilis, Heller, 1866; T. willemoesii, Studer, 1884; T. hirsutus, Beddard, 

 1886 ; and since Sars wrote, several additions have been made to the list, namely, 

 T. robustus, Moore, 1894; T. grimaldii, Dollfus, 1897; T. chevreuxi, Dollfus, 

 1897; T. testudinicola, Dollfus, 1897; T. alascensis, H. Richardson, 1899; 

 T. stamfordi, H. Richardson, 1901; T. philetcerus, Stebbing, 1904; T. normani, 

 H. Richardson, ] 905. In this group it must be noticed that brasiliensis, gracilis, 

 willemoesii, hirsutus, robustus, testudinicola, normani, are all excluded from the genus, 

 not as defined by Dana, but as restricted by Sars, since they all have six segments 

 in the pleon instead of five. It is not improbable that other more or less correlated 

 differences will be found to exist, but the material here at disposal would not justify 

 interference in the matter. It may, however, be observed that T. testudinicola, 

 Dollfus, is evidently the same species as T. robustus, Moore. T. loricatus, Bate, 

 described from an imperfect specimen, still awaits fuller description. T. vovcb- 

 zealandice, G. M. Thomson ('Trans. N. Zealand Institute,' vol. 13, p. 207, plate 7, 

 fig. 3), according to the figure, has the pleon distinctly six-jointed, but no notice of 

 this is taken in the text, which includes in the generic definition the character " pleon 

 five-jointed." 



