SIRIELLA AND GASTROSACCUS 277 



precedlDg species, while the telson terminates * in a 

 small spinule flaDked on each side by the usual setce, and a 

 more mioute spinule between the ultimate pair of spines.' 

 4. Siriella Broohi, Norman, which seems to be intermediate 

 between Siriella Glausii and Siriella jaltensis, having the 

 single antennular seta of the former, and the apex of the 

 telson armed as in the latter, the legs also being of inter- 

 mediate thickness. 5. Siriella armata (Milne-Edwards), 

 which is distinguished by an elongate rostrum reaching 

 the end of the second joint of the first antennas, and by the 

 telson 'terminating usually in four equal-sized spinules 

 and two set^e between the ultimate spines.' In Norman's 

 opinion both Mysis Griffithsice, Bell, and Mysis x>rod%ictm 

 (Gosse) may be synonyms either of this or of the next 

 species. Pf<ei(dosiriella, Glaus, was instituted to receive the 

 species Mysis frontalis^ Milne-Edwards, which Sars had 

 previously transferred to Siriella. It has a well-developed 

 rostrum like Siriella armata^ but the appendages, to which 

 a branchial function has been attributed, on the pleopods 

 of the male, are here simple instead of being coiled. Ac- 

 cording to Ganon Norman, Pseudosiriella frontalis belongs 

 to the British as well as the Mediterranean Fauna. 



Gastrosaccus, Norman, is distinguished by the laterally 

 compressed carapace, and in the female by the great de- 

 velopment of the side-plates of the first pleon-segment 

 which appear to assist the marsu23ium in the retention of 

 the eggs. The marsupial plates are two pairs, the first 

 pair being very small and sending a strap-shaped setiferous 

 process into the cavity of the pouch. The first pleopods in 

 the female are very large, the rest very small. All the 

 pleopods of the male are biramous and at least in part 

 natatory. The telson is apically incised. Gastrosaccus 

 sanctus (van Beneden) is found in the Mediterranean, on 

 the Belgian and French coasts, and at Jersey. Gastrosaccus 

 spinifer (Goes) is found both in the Baltic and on the coasts 

 of Great Britain, and is distinguished from the preceding 

 species by the dentately fringed hind margin of the carapace 

 and by a w^ell-developed dorsal spine on the fifth pleon- 

 segment. 



