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joint of the left exopodite is distinctly notched. The apical spines are short and stout. The 

 longer one is considerably shorter than the joint (Plate XLIY, fig. 1 7). 



The rounded last thoracic segment, and the long furcal joints readily separate this form 

 from any of the other known species. 



The female described by Esterly as Arietellus major appears to be identical with Sars' 

 Arietellus simplex. The figure of the fifth foot given by Esterly, and reproduced in this 

 report, shews the apical spine of the second free joint to be very short. It is only about equal 

 to one-half of the length of the joint. 



Genus Paraugaptilus Wolfenden, 1904. 



This genus was established by Wolfenden in 1904, for a form found in the warm area 

 of the North Atlantic, that appeared to be closely related to Augaptilus and Arietellus. Sars 

 (1907 a) recorded Wolfenden's type species from the plankton collected by the Prince of Monaco, 

 but placed it under the genus Arietellus. Van Breemen, however, regards the genus as distinct 

 and restores it in 'Nordisches Plankton' 1908. This genus appears to be more closely related 

 to Arietellus than to Augaptilus. I have therefore included in under the Family Arietellidae. 



The two sexes are readily separated from either Augaptilus or Arietellus, by the structure 

 of the fifth pair of feet. The fifth pair of the female is rudimentary. Each foot is composed 

 of a single joint. The male fifth pair is well developed and prehensile. The right and left 

 feet are not symmetrical. The basiopodite is two-jointed. The exopodite of each foot is two- 

 jointed. The endopodite is very small. It is apparently two-jointed. 



Males and females of a form closely related to the type of the genus were obtained 

 from the plankton collected by the 'Siboga' in the Malay Archipelago. 



1. Paraugaptilus siwilis nov. sp. Plate XLIII, figs. 11 — 19. 



Female — length 3,75 mm. 



Viewed from above, the body appears ovate and robust. The forehead is considerably 

 contracted in front. The posterior margins of the last thoracic segment are broadly rounded. 

 The segment is furnished with a small tooth on each side of the junction with the abdomen. 

 Seen from the side, the dorsal surface of the cephalic segment is much depressed, and the 

 forehead is very narrowly rounded. The ventral margin of the last thoracic segment is boldly 

 rounded. The distal end is hollowed out. It is produced into a small tooth at the upper angle, 

 where it joins the dorsal line (Plate XLIII, fig. 13). The dorsal and lateral surfaces of the 

 thoracic segments, are clothed with fine short hairs as shewn in the figures. The rostrum is 

 represented by two slender filaments. 



The abdomen is composed of four segments. The combined length of the abdomen 

 and furca is contained two and a half times in the total length of the ecphalothorax, from 

 the frontal margin to the base of the genital segment. The genital segment is moderately large. 

 It is distinctly inflated on each side. The lateral surface is furnished with a small, dorsally 

 directed pointed process. The genital opening is provided with a pointed knob (Plate XLIII, 



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