2l8 



One species, apparently undescribed, but agreeing with Brady's definition of the genus, 

 was obtained from the plankton collected by the : Siboga' in the Malay Archipelago. 



i. Pseudothalestris sarsi nov. sp. Plate LXIII, figs. i — 7. 



Female — length .68 mm. 



Seen from the side, the body appears short and moderately robust. The cephalic segment 

 is large and exceeds the combined length of the thoracic segments. The rostrum is very short 

 and is triangular in shape. 



The abdomen is composed of four segments. The genital segment is longer than the 

 combined length of the next three segments. The anal segment is much shorter than the other 

 segments. The furcal joints are shorter than the anal segment. Each joint is one and a half 

 times broader than long (Plate LXIII, fig. 7). 



The antennules are comparatively short and six-jointed. The fifth joint is shorter than 

 any of the others. 



The antennae, mandibles, maxillae and maxillipedes are similar to those of Pseudothalestris 

 imbricata Brady. 



The exopodite of the first pair of feet is short and is distinctly two-jointed. The joints 

 are sub-equal in length. The endopodite is composed of three joints and is equal to two and 

 a half times the length of the exopodite. The first joint is very long. The second and third 

 joints are exceedingly short. The apex of the third joint is furnished with one long and one 

 very short claw, and a small seta (Plate LXIII, fig. 5). 



The second, third and fourth pairs of feet are similar to those of Pseudothalestris 

 imbricata Brady. 



The fifth pair of feet is comparatively large. The proximal joint is greatly expanded. 

 The apex is armed with five moderately strong spines of unequal length and four small setae. 

 The distal joint is small and is somewhat quadrangular in outline. It is furnished with one 

 outer marginal spine, one inner marginal spine, and one apical spine. The distal end of the 

 inner margin has also two short setae (Plate LXIII, fig. 6). 



Male unknown. 



This species resembles Pseudothalestris major T. and A. Scott (1895), in general 

 appearance, but it can readily be distinguished from it or any of the other members of the 

 genus by the proportional length of the joints of the antennules, and by the shape and armature 

 of the fifth pair of feet. Sars, 'Crustacea of Norway' Vol. V, p. 143, regards Pseudothalestris 

 major to be identical with Westwoodia minuta Claus (1863). This view cannot very well be upheld 

 because Claus in his generic description of Westwoodia defines the exopodite of the first pair of 

 feet to be short and one-jointed. Pseudothalestris major has the exopodite distinctly two-jointed. 

 The shape and armature of the fifth pair of feet illustrated by Sars as that of the female of 

 Westwoodia 'minuta Claus, is quite different from the figure of the same pair of Pseudothalestris 

 major given by T. and A. Scott in the 'Annals and Magazine of Natural History, Ser. 6, 

 £V, January 1895. Sars states that Westwoodia minuta Claus, has six-jointed antennules. 



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