SIRIELLA AND GASTROSACCUS pa 
preceding species, while the telson terminates ‘in a 
small spinule flanked on each side by the usual setae, and a 
more minute spinule between the ultimate pair of spines.’ 
4, Siriella Brooki, Norman, which seems to be intermediate 
between Siriella Clausii and Siriella jaltensis, having the 
single antennular seta of the former, and the apex of tke 
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 antenna, and by the - 
telson ‘terminating usually in four equal-sized spinules 
and two sete between the ultimate spines. In Norman’s 
opinion both Mysis Griffithsice, Bell, and Mysis productus 
(Gosse) may be synonyms either of this or of the next 
species. Pseudosiriella, Claus, 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 Canon 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 marsupium in the retention of 
the eggs. ‘The marsupial plates are two pairs, the first 
pair being very small and sending astrap-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.  Gastrosuccus 
sunctus (van Beneden) is found in the Mediterranean, on 
the Belgian and French coasts, and at Jersey. Gastrosaccus 
spinifer (Goés) 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 well-developed dorsal spine on the fifth pleon- 
segment. 
