LARVAE OF SERGESTES 47 



are separated out, it is found that they have a very close general similarity. They all 

 agree in having the same form of eye, though differing in length of eyestalk ; in having 

 the uropod very slender and the setose part of the margin i| or more times longer 

 than the bare part ; in having the lateral spine of somite 5 (and usually of 4 also) very 

 short and simple, and in the presence of median ventral spines, or prominent papillae, 

 on two or more of the abdominal somites. 



Among the specimens of this group at our disposal four quite distinct species can 

 be separated. One of these is S. vigilax; but the identity of the others is less certain. 



We feel little doubt that we have correctly named the larvae of S. edzvardsi, and the 

 identification of S. armatus, though less secure, seems most probable, especially in view 

 of the fact that Hansen mentions the presence of ventral spines on somites 1-3 of the 

 Mastigopus. 



If these species are accepted the fourth must belong to S. diapontius, but the identifi- 

 cation by exclusion in this way is not very satisfactory, in view of the possibility that 

 there may be other adult species still undescribed. 



Sergestes pectinatus Sund 



Hansen, 1822, p. 146, Mastigopus. 



Cecchini, 1928a, fig. 3«; 19286, pi. 2, fig. 4, Acanthosoma 2. 



Illig, 1927, p. 319, S. hemeni, Mastigopus, fig. 84 (?); p. 331, S. tiudus, Mastigopus, fig. 104 (?). 



Material. This is one of the commonest species at Bermuda, occurring as larva or 

 Mastigopus in depths from surface to 300 metres. The Acanthosoma has been identified 

 by moulting to Mastigopus, and the Elaphocaris is attributed to it by its resemblance 

 to the Acanthosoma in colour, size and shape of eye. 



Description. Elaphocaris 3 (Fig. 38 a). Length 1-12 mm. Rostrum 0-64 mm. 



Rostrum denticulate. Supraorbital processes long and thin, branching into four 

 spines, one thinner than the others. Lateral processes long, denticulate at tip, with a 

 basal epaulette of eight spines. Dorsal process springing from a rounded base with 

 four spines. Dorsal organ very small. 



Abdominal somites with sharp lateral spines, the first three directed backwards. 

 Telson with thick short branches and four long denticulate spines, and two very small 

 spines. The first long spine directed forwards, the others backwards, very long and 

 almost parallel. 



Eye short, very large, the greatest width of eyeball exceeding length of eye. 



Colour. Red at sides of carapace and abdomen and on eyestalks. 



Acanthosoma i (Fig. 38 b). Length 2 mm. Rostrum o-8 mm. 



Rostrum much longer than antennule. Carapace broader than long, with a con- 

 spicuous angular prominence behind the anterior lateral spine. Supraorbital spine as 

 long as eye. Hepatic spine small and simple. Anterior lateral spine very long and prickly ; 

 posterior lateral spine very small and springing from the dorsal surface. Posterior dorsal 

 spine very small. Dorsal organ very large, conical. 



