AMPHIPODA OF THE SCOTTISH NATIONAL ANTARCTIC EXPEDITION. 201 



Thaumatelson inermis, sp. nov. (PI. I. figs. 16 and 17.) * 



South Orkneys, Scotia Bay, Station 325 ; 9-10 fathoms. April and May 1903. 

 Several specimens, the largest 3 mm. long. 



Specific Description. Very similar to T. herdmani Walker, but differing in having 

 the second gnathopod long and chelate, the propod being produced into a long acute 

 process as long as half the whole propod, the fixed finger finely pectinate and fitting 

 closely against the dactyl, which has its inner margin furnished with small, widely 

 separated serrations. 



Further Description. The form described above is the female, several of the speci- 

 mens examined bearing eggs. The lateral angle of the head is rather acute ; and in the 

 shape of the body, the proportions of the segments and of the side plates, the species 

 closely resembles T. herdmani. The eye is fairly large, round, and colourless in spirit, 

 having been probably red in the living animal. In the first antenna the first joint is 

 large and produced at its upper distal angle, though to a slightly less extent than in T. 

 ivalkeri, and I can find no accessory Hagellum. In other respects the antenna is similar 

 to that of T. herdmani, and the joints of the flagellum bear long sensory setae. In the 

 lower antenna the last joint of the peduncle is about as long as the preceding, and the 

 Hagellum is of the same length. The mandible has the palp small, the first joint is 

 short, the second moderately long, the third small and slender, the cutting edge and 

 other parts having the character common to the family. The first maxilla has the 

 palp two-jointed, its extremity furnished with four or five small spinules and one or 

 two longer sette ; the inner lobe is rounded at the end, and bears three or four setae ; the 

 outer lobe bears several stout spinules and one or two longer setae, and has its inner 

 margin furred. The second maxilla is of the ordinary form. 



The maxillipeds have the inner lobes separate, rounded at the end, and bearing 

 two rather large setae. The outer lobe is small, being merely a slight extension of the 

 joint as in Metapoides sarsii. The palp is similar to that in T. herdmani. 



The first gnathopod (fig. 16) has the side plate undeveloped; in general shape it 

 is similar to that of T. herdmani, but has both the rnerus and the carpus produced 

 posteriorly into a lobe tipped with long setae, the process of the merus reaching to the 

 end of that of the carpus. The propod is rather large, and is slightly distended at the 

 palm, which is nearly transverse and is defined by three or four stout spinules. 



The second gnathopod (fig. 17) has the basal joints similar to those of T. herdmani, 

 but is chelate, as already described. The peraeopoda are long, very slender, and bear 

 few setae or spinules. The side plates of the fourth pair are particularly large, and 

 cover up the fifth, sixth, and seventh pairs, the side plates of which are not developed 

 and the basal joints slender. The first uropod extends considerably beyond the second ; 

 the branches are subcqual, shorter than the peduncle. The second uropod is short, but 

 extends beyond the third and a little beyond the telson ; its branches are subequal. 



* This species is perhaps the same as Thaumatelson nasuttim Chevreux (Bull. Museum Hist. Nat., 1912, No. 4, 

 p. 5), though the descriptions of the mandibular palp do not agree. 



(ROY. soc. EDIN. TRANS., VOL. XLVIII., 483.) 



