COPEPODA 



89 



23. Gaidius tenuispinus G. O. Sars. 

 (PI. II fig. 8 a; pi. Ill figs 2 a n; text-figs 23 a j). 



1900. Chiridius tenuispinus n. sp. G. O. Sars, p. 67, pi. XVIII. 

 1902. Gaidius tenuispinus G. O. Sars. Mrazek, p. 512. 



1902. borealis n. sp. Wolfenden, p. 365. 



1903. tenuispinus G. O. Sars. Norman, p. 136. 



1903. Chiridius tenuispinus G. O. Sars. G. O. Sars, pp. 30 31, 



pi. XVIII. 



1903. Gaidius tenuispinus G. O. Sars. G. O. Sars, p. 162, pi. VI, 



suppl. 



1904. PGaidius pungens Giesbr. Wolfenden, p. 131, pi. IX fig. 43. 



1905. Chiridius tenuispinus G. O. Sars. Th. Scott, p. 223. 



1905. Gaidius tenuispinus G. O. Sars. Farran, p. 33. 



1906. Pearson, p. 13. 



1907. Gaidius tenuispinus G. O. Sars. Vanhoffen, pp. 521 522, 



taf. 21 fig. 27, taf. 22 fig. 33. 



1907. G. O. Sars. Koefoed & Damas, p.4o8. 



1908. Karran, p. 32. 



1908. v. Bremen, p. 36, fig. 39. 



1909. Nee. similis Th. Scott. A.Scott, pp. 5152, pi. VII 



figs i II. 



1911. tenuispinus G. O. Sars, Farran, p. 97. 



1911? Wolfenden, p. 223, figs 



II a b. 



1913. Stephensen, pp. 315 



-316. 



Description. f$. Size: Specimen from Thor St. 70 measured 3-84 mm.; anterior division 2-94 mm.; 

 urosome 0-90 mm. Two specimens from Thor St. 285 measured 2'6 -f- 0-62 = 3-22 mm. and 2-9 -|- 0-8 

 = 37 mm.; specimens from Thor St. 183 measured 27+07 = 3-4111111. Sars' specimens measured 3-8 

 and Wolf en den's 3-8(1904) and 3-25 (1911) mm. Van ho f fen's specimens 3-9 and Far ran' 5(1905) 3-2 mm. 



The shape of the body is scarcely different from Sars' figure, and no trace of segmentation 

 between the fourth and fifth thoracic somite was observed; the lateral spines of the thorax are distinctly 

 set off, and extend almost to the end of the genital somite (text-fig. 23 a). The rostrum is not, as set 

 forth by most authors, undivided, but shows as seen in fig. 2 a (PI. Ill) trace of bifurcation. 



The length of the abdomen, compared to that of the anterior division, varies from about '/ 3 

 to x /4- The genital somite, which as seen in fig. has a short and well marked receptaculum seminis, 

 well distinguished from the stalked one in Chiridius, is somewhat deeper and wider than long, and 

 [-6 as long as the third somite. The furcal rami are 1-6 as long as wide and a little wider than the 

 anal somite is long. 



The antennulae reach to about the end of the third abdominal somite and have the measure- 

 ments distinctly different from those of G. brevispinus on account of the shorter distal segments; the 

 segment 2 is ra as long as 8029, which is almost 1-3 as long as segment 13 and only a little shorter 

 than segment 20; the segments 19 and 22 are almost of equal length, and almost ri shorter than 

 segment 2. The appendages are like those described by Giesbr edit in Gaetanus armiger with 

 "Aesthetasken" in segments 3, 4 and 6 and Spr. in segment 13; the posterior seta of the segment 23 

 is ringed, and about three times as long as the segments 24 and 25, which are well separated. 



The antennae have the Re 1-3 as long as Ri; the Ri I is distinctly twice as long as Re II; 

 this, is about twice as long as Re I, and about twice as long as Re III VI, and about 2 / 3 as long as 

 Re VII. The Re II has the short Se 2 placed on a rather prominent process, (PI. Ill fig. 2 e), like 

 that found in Giesbrecht's fig. 19 Taf. 14 of Gaetanus armiger, and the Se 3 is somewhat longer. 

 The mandibulae differ from Sars' figure by two slender Si of the third basipodite, and are in main 

 features like those in Giesbrecht's G. armiger. The maxillulac are rather elongated, like Gies- 

 brecht's figure of Gaetanns miles (Taf. 14 fig. 21); the Li I possesses on the anterior surface about 10 

 fairly strong teeth, and on the posterior surface near the base of S n about 10 similar ones; the Li II 

 has 4 setae, and the Li HI 5 -f- a sensory lobe and anteriorly a fairly strong spinulation, the Basp. Ill 



The Ingolf-Expedition. III. 4. 12 



