260 Records of the Indian Museum. [Vol. XXIV, 



Borradaile distinguishes the genus from Anchislus by the 

 greater proportionate breadth of the two distal segments of the 

 third maxilliped ; they are, however, slender in at least one species 

 of Pontonia. 1 His statement in the generic diagnosis that the dac- 

 tylus of the last three legs is simple is evidently a lapsus calami, 

 for it is biunguiculate in P. tyrrhena and in the majority of the 

 species. 



Nobili 2 has pointed out that Forskal's Cancer custos 3 was 

 obtained in a species of Pinna in the Red Sea and that the name 

 cannot be applied, as it frequently has been, to the Mediterranean 

 species more properly known as Pontonia tyrrhena. On the Indian 

 coasts two Pontoniine prawns are found in Pinna, viz. Anchistus 

 inermis (Miers) and Conchodytes biunguiculatus (Paulson). Both of 

 these, if my identifications are correct, also occur in the Red Sea, 

 but Forskal's description is too indefinite to enable us to decide 

 which was the original of his C. custos. Nobili, moreover, is of the 

 opinion that the name custos is preoccupied by Forskal's own use 

 of the term on p. 89 of his work in reference to a Pinnotheres. 



To the genus Pontonia Borradaile assigns ten species, but of 

 these Ortmann's P. pinnae, as Tattersall has suggested, is synony- 

 mous with Anchistus inermis, while Parisi has pointed out that 

 P. nipponensis de Haan belongs to the genus Conchodytes. Two 

 species from the W. Coast of America are to be added to the 

 genus: P. pinnae Iyockington* {nee Ortmann), which Borradaile 

 appears to have overlooked, and P. margarita Smith 4 which he 

 refers to the genus Conchodytes. 



Only four species have hitherto been recorded from the Indo- 

 Pacific region, viz. P. brevirostris Miers 6 from the Seychelles in 

 " clamp shells," P. ascidicola Borradaile 8 from New Britain in a 

 ascidian, P. minuta Baker 1 from S. Australia, a species of un- 

 known association, and P. quadratophthalma, also of unknown 

 association, recently described by Balss 8 from N.W. Australia. 



I have seen only two Indo-Pacific species of this genus, both of 

 which appear to be undescribed. They are related to P. ascidicola 

 and were found lodged in the branchial sac of simple ascidians. Dr. 

 Asajiro Oka, who found these specimens when examining the 

 Indian Museum collection of Tunicata, remarks that judging from 

 their size they ' ' must have entered the body of the host as larvae 

 and grown up there to maturity. 9 ' ' 



The six Indo-Pacific species of Pontonia may be distinguished 

 by the following characters : — 



1 P. okai, sp. nov. 



2 Nobili, Bull. sci. France Belgique XI., p. 49 (1907). 



3 Forskal, Descr. Anini., p. 94 (1775). 

 * See Addendum, p. 287. 



6 Miers, Zool. Coll. H.M.S. 'Alert/ p. 562, pi. li, fig. B (1884). 



'*> Borradaile, in Willey's Zool. Results, p. 409, pi. xxxvi, figs. 6a, b (1Q02). 



7 Baker, Trans. R. Soc.S. Australia XXXI, p. 189, pl.xxiv, figs. 9-12 (1907). 



8 Balss, K. Svenska Vet.-Akad. Handl., LXI, no. 10, p. 15, text-fig. 7 (192 1). 



9 Oka, Mem- hid. Mus. VI, p. 2 (1915). 



