NO. 26 NEW MYSIDACID CRUSTACEANS TATTERSALL 9 



Pleopods of the male with both rami of the third and fourth pairs 

 with modified setae on the terminal and penultimate joints. In the 

 third pair the terminal joint of the endopod (text fig. 3c) bears two 

 modified setae, a large, blunt simple one and a smaller, more acute 

 plumose one. The exopod of the third pair (text fig. 3d) has a pair 

 of similarly modified setae, both plumose, on the terminal joint. In 

 the fourth pair the endopod (text fig. 3^) has the terminal joint 

 furnished with two modified setae, the longer very closely and finely 

 feathered but much stouter than the normal plumose setae arming 

 the rest of the limb, the shorter stout and simple ; the penultimate joint 

 has one of its plumose setae modified in the same way as the longer 

 of the two setae on the terminal joint, that is, it is stouter and more 

 closely and finely feathered. The exopod of the fourth pair (text 

 fig- 3/) has the terminal joint armed with one long, stout, simple 

 spiniform seta and a rather short, fine, simple seta; the penultimate 

 joint, in addition to the normal plumose seta at each distal corner, has 

 a single long, stout, simple seta inserted some little way behind the 

 distal margin on one side. 



Length of adult specimens of both sexes, 10 mm. 



Ty/*^.— U.S.N.M. no. 72867. 



Remarks. — In the group of species of Siriella to which this species 

 belongs S. occidentalis is distinguished by having both the third and 

 fourth pleopods of the male furnished with modified setae. Only one 

 other species, 5". anoutala Hansen, has both third and fourth pleopods 

 of the male modified in this way. vS*. anomala, however, has the pseudo- 

 branchial rami of the second to the fourth pleopods of the male nearly 

 straight and not spirally twisted as in S. occidentalis. 



Otherwise 5*. occidentalis is very closely allied to the other species 

 within its group, especially to ^. inornata Hansen, and can only be 

 certainly determined from an examination of adult male specimens. 

 The species is apparently a very abundant one in the inshore waters 

 of the islands of the West Indies. 



Subfamily Gastrosaccinae 



GASTROSACCUS Norman 



GASTROSACCUS JOHNSONI, n. sp. 



Text figs. 5-7 



Localities. — Serial numbers 358 B, 387 B, 406, 407 B, 521. 

 Description. — Carapace (text fig. 5a) produced in front into a short 

 triangular rostral plate with a subacute rounded apex ; dorsal posterior 



