70 DISCOVERY REPORTS 



The Discovery material contains some specimens which closely conform to the description and 

 figures which Illig had given for the males of B. rostrata and I have followed Tattersall's suggestion 

 and founded a new species, B. illigi for them (see p. 72). 



Even within the narrower definition of B. rostrata, Tattersall found that considerable variation 

 occurred. He recorded: 'The female specimens have a longer rostral process than the male though in 

 no case is it as long as shown by Illig. Incidentally the rostral plate is relatively longer in young 

 specimens than in adults and appears to undergo progressive reduction with growth.' 



In the Discovery collection I have not found such a definite sexual difference as Tattersall de- 

 scribed, although a considerable amount of individual variation in the length of the rostrum exists. 

 At station WS 748 many adults of both sexes occurred, among which no appreciable difference in 

 rostral length was found. At stations 78 and 87, however, specimens showed definite sexual 

 differences and in all the females the rostrum was longer than in the males. The collection provided 

 additional evidence of the growth changes which were noted by Tattersall. In immature specimens 

 from stations 942, 1566 and 1753, the rostrum was long and extended forward beyond the anterior 

 margin of the cornea. 



The specimens, which I have here referred to B. rostrata Illig, show a certain amount of deviation 

 from the description given by Illig (for his females) in the length of the rostrum and the apex of 

 the antennal scale and considerable variation in the relative size of the eyes. I have examined the rich 

 Discovery collection with the greatest care and find that the animals show every gradation in these 

 characters, it being quite impossible to separate them into definite groups. I have tried, with very 

 little success, to correlate the variations with geographical distribution, since wide variation may occur 

 among individuals from the same localities. In view of the very constant form of the tail fan, the endo- 

 pods of the thoracic appendages and the pleopods, I feel that the simplest solution is to refer them all to 

 rostrata and to accept a certain amount of latitude in the definition of that species in respect of these 

 variable characters. I therefore put forward the following five definitive characters as a guide to 

 identification: (1) rostral process of the male relatively short, usually shorter than the eyes, with 

 acutely pointed apex and anterior margin of carapace with no definite ' shoulders ' ; of the female, long 

 and acutely pointed and no trace of ' shoulders ' ; (2) large eyes with well-developed ocular papilla and 

 cornea wider than eyestalks; (3) a non-chelate termination to the endopod of the second thoracic 

 appendage; (4) a long telson with the spines arming the lateral margins arranged in series, cleft 

 narrow and marked by a distinct 'dilatation' at its base; (5) unarmed portion of the outer margin of 

 the exopod of the uropod very short. There is, however, much variation in all these characters. 



The uropods are very long and slender with the exopod only slightly longer than the endopod. The 

 unarmed portion of the outer margin of the exopod of the uropod is only one-tenth, or less, of the 

 total length and is terminated distally by a single small spine. The endopod is armed on its inner 

 margin, just distal to the statocyst, with a single long, slender, curved spine. The telson is quite charac- 

 teristic, long and narrow, equal in length to the last three abdominal somites together. The lateral 

 margins are unarmed for the proximal fourth of their length, the remaining three-fourths being densely 

 armed with a series of eight to ten long, strong spines with graduated series of from four to eight small 

 spines in the spaces between them. The cleft is deep and narrow with a characteristic dilatation at 

 its base. 



In most of the specimens the eyes are as figured in Illig's type, but the relative size varies 

 considerably. The colour of the pigment in these preserved animals ranges from black to golden 

 brown. 



Hansen (1910, p. 26) founded a new species, B. inermis, on a single male specimen from near the 

 Dutch East Indies. Tattersall (1951, p. 57) pointed out that the only real difference between this 



