EUPHAUSIA LUC ENS 205 



They were as follows: 



At five stations : At one station : 



E. vallentini E. vallentini 



E. triacantha E. triacantha 



E. longirostris E. similis 



E. similis E. lucens 



E. frigida E. frigida 



The complicated copulatory organs of the males of the different species show constant 

 and unmistakable differences and form the most reliable criterion for separating them. 

 In the accounts of the organs that follow under each species more details are given than 

 are necessary for their recognition, and than would be seen under the low power of a 

 binocular microscope — indeed the figures alone are sufficient for recognition. The 

 details have been given because they are necessary for the comparative account of the 

 copulatory organs which follows (pp. 244-252) ; in it the ten species are divided into two 

 groups, and it is suggested that the male copulatory organs show that the members of 

 each group are related to one another as the members of an evolutionary series. 



Hansen (1910, p. 79) says of the copulatory organs that "in all species (oi Euphausm) 

 hitherto examined by me a spine-shaped process on the inner lobe and additional 

 processes on the median lobe are totally wanting". But in a later paper (1912, p. 230) 

 he records seeing the spine-shaped process in one specimen oi E. lucens and says that the 

 additional process is present as a small spine in E. miicronata and as a mere rudiment in 

 E.gibboides. Zimmer (1913, p. 117, pi. xiii, fig. 72, />.«.) says that he found in the speci- 

 mens of E. siiperba he examined indications of the additional process on the median lobe 

 in the form of a tiny spine. 



I have seen a very small spine-shaped process on the inner lobe in two or three 

 specimens of E. siiperba, but not in E. lucens nor in any of the other species. I find a 

 small additional process on the median lobe to be present in every one of the ten species 

 except E. lucens ; in one specimen of E. superba there were two additional processes on 

 the median lobe. 



Euphausia lucens, Hansen (Figs. 7-1 1 and 30 a) 



E. lucens, Hansen, 1905, p. 9; 1911, p. 26, fig. 8; Tattersall, 1913, p. 876; Hansen, 1915, p. 84; 



Zimmer, 1915, pp. 178-9; Colosi, 1917, p. 183, pi. xiv, figs. 6-8; Tattersall, 1924, p. 19; 



Illig. i930> P- 499; Tattersall, 1925, p. 6; Hardy and Gunther, 1935, p. 208. 

 E. splendeiis (part), Sars, 1885, p. 80, pi. xiii, figs. 7-17. 

 E. iincinata, Colosi, 1917, p. 186, pi. xiv, figs. 9-10. 



Description. The front margins of the carapace are very faintly convex behind each 

 eye; the rostrum is a small broad triangle (Fig. 7). 



In the antennule the lobe from the end of the first segment of the peduncle is triangular 

 and variable in size ; it may be very short, a small wide triangle, or it may be a long thin 

 triangle one-third as long as the second segment of the peduncle. It is easily seen from 

 the side. The dorsal keel of the third segment is strong ; as seen from the side it appears 

 to rise a little less than half-way along the segment ; its upper margin is nearly straight 

 or slightly curved. 



