46 DISCOVERY REPORTS 



absence of a spine or thorn at the distal end of the naked portion of the outer margin of the antennal 

 scale, by the persistence of colour in the cornea of the eye even after prolonged preservation, by the 

 shorter, more robust endopods of the 2nd to the 4th thoracic appendages and by the presence on the 

 eighth thoracic appendages of well-developed branchiae (borne in front of the appendage instead of 

 behind, as in the other limbs). The distinctive shape and ornamentation of the telson, whereby larger 

 animals can at once be identified, does not develop until a length of 12-15 mm. has been reached 

 and even in specimens of 20 mm. the well-known constrictions of the telson and its honeycomb 

 ornamentation are only faintly marked. 



Identification of the other three species presents greater difficulty. Owing to the softness of the 

 integument and the fragility of the animals, well-preserved specimens are rarely obtained. Even in 

 the extensive Discovery collections, I found (as have so many previous workers on other material) 

 that, among all the hundreds of specimens of Eucopia, there was not one undamaged individual nor 

 a single female with eggs or embryos in the brood sac. 



The size of adult animals is one of the most useful guides in the separation of australis, unguiculata 

 and grimaldii, although it must be borne in mind that in all three species the animals tend to be more 

 precocious in warmer waters. In the Discovery collection females of australis 37-44 mm. in length, 

 have small, not fully developed oostegites with the fringes only just beginning to appear and at station 

 245 a specimen of 47 mm. was still immature. At station 2065, however, a female of 45 mm. had fully 

 developed oostegites. The average size of adult females of australis is 51 mm. E. grimaldii is a smaller 

 form than australis ; females of less than 27 mm. are quite immature and fully adult specimens range 

 from 29 mm. to 38 mm. E. unguiculata is definitely a smaller, more slender form than either of the 

 preceding species; females of 17 mm. to 23 mm. are immature but have well-formed oostegites and 

 adult females range from 22 mm. to 29 mm. 



Text-figs. 4-5 show the anterior end, the telson and a uropod of each of the three species. In the 

 case of australis I have figured what might be described as an average specimen, for nearly all the 

 animals which I have referred to this species have the telson as in Fig. 4D. However, there are a few 

 individuals which, while agreeing with australis in all other respects, have the spines arming the telson 

 arranged more like those of grimaldii. Other specimens show some characters intermediate between 

 australis and unguiculata or grimaldii, affording further evidence of the variability of the three species. 



Hansen (1910, p. 21) separated a species, E. major, from E. australis on three characters: (1) its 

 smaller size, (2) eyes scarcely twice as long as broad, (3) terminal segment of the exopod of the uropod 

 broader than long. In 1912 (p. 188) he referred specimens of over 60 mm. captured by 'Siboga', 

 to E. major, and, although they were as large as adults of australis, he considered that the other charac- 

 ters were sufficient to justify the species. Fage (1942, p. 40) pointed out that the species australis 

 possessed particularly thin chitin and that, since the animals were bathypelagic, the net brought them 

 to the surface in poor condition. Consequently, accurate measurement of the various parts was very 

 difficult, the eyes in particular being very distorted. Fage therefore considered that Hansen (1910) 

 was not justified in separating the species E. major from E. australis. 



Nouvel (1942 a, b; 1943) followed Hansen in regarding the length/breadth ratios of the eye, the 

 distal segment of the antennal scale and the distal segment of the exopod of the uropod as of specific 

 significance. These characters are extremely variable and, after examining the Discovery material I can 

 fully endorse Fage's opinion and I accept his view that E. major and E. australis are synonymous. Of 

 seventy-five measured adult specimens, only eight could with certainty be referred to australis on 

 Hansen's diagnosis and seven to major. It is obvious that these characters are too variable to be of 

 specific value. Nor can the variations be attributed to geographical location, for the same diversity 

 occurs among individuals in the same haul. My measurements are given in Table 3. 



