2 14 



This species is readily recognised by the shape of the genital segment and furcal joints, 

 and also by the comparatively slender form of the fifth pair of feet. 



Porcellidium brevicaudatum has only previously been recorded from Ceylon. 



29. Family Thalestridae. 

 Genus Phyllothalestris G. O. Sars, 1905. - 



Professor G. O. Sars has separated Thalcstris mysis from true Thalestris on account 

 of the enormous development of the fifth pair of feet of the female, and has established it in 

 a distinct genus. 



One species is knovvn. It was represented in the plankton collected by the 'Siboga' in 

 the Malay Archipelago. 



1. Phyllothalestris mysis (Claus). Plate LXII, figs. 1 — 5. 



Thalestris mysis Claus, 1863, p. 130, pi. XVIII, figs. 12 — 16. 



Thalestris mysis Brady, 1880, vol. II, p. 121, pi. LVIII, figs. 1 — 3. 



Thalestris mysis T. Scott, 1901 (<z), p. 354. 



Thalestris mysis Thompson & Scott, 1903, p. 272. 



Thalestris mysis Pearson, 1905, p. 13. 



Phyllothalestris mysis Sars, 1905, p. 116, pis. LXX & LXXI. 



Phyllothalestris mysis T. Scott, \go6(a), p. 314. 



Phyllothalestris mysis Norman & T. Scott, 1906, p. 168. 



Two females identical with the above species were obtained from the plankton collected 

 at the surface at Station 142, when the 'Siboga' was at anchor at Laiwui. 



The illustration of the fifth pair of feet given on Plate LXII, fig. 5, is similar in shape 

 to the figure given by Sars in 'Crustacea of Norway' Vol. V. The surface of the fifth pair of 

 the 'Siboga' specimens is marked by numerous interrupted transverse lines as shewn by the 

 figure. Length of 'Siboga' specimens 1,9 mm. 



The very large foliaceous fifth pair of feet is a conspicuous character and enables the 

 species to be readily recognised. 



Phyllothalestris mysis appears to be rather widely distributed. It has been recorded 

 from the British and Norwegian Coasts, from the Mediterranean, from the Gulf of Suez, and 

 from the Island of Ceylon. 



Genus Rhynchothalestris G. O. Sars, 1905. 



The members of this genus can be distinguished by the unusually sharp division between 

 the cephalothorax and the abdomen, and by the very large rostrum. 



Two species were represented in the material collected by the 'Siboga' in the Malay 

 Archipelago. One of the species does not appear to have previously been described. 



214 



