6 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. QI 



It should be remarked that P. glaber and P. macrops are very closely 

 similar and differ mainly in the form of the rostral plate. Hansen has 

 figured the rostral plate of a half-grown specimen of P. glaber in 

 which the rostral plate is exactly as figured for P. vmcrops by Colosi, 

 that is, the central tooth of the trident is missing and the front margin 

 is slightly convex with a tooth at each corner. Hansen gives the size 

 of adult specimens of P. glaber as i8 mm, whereas P. macrops was 

 founded on specimens 12-13 ^^"^ ^^ length. It is not unlikely that 

 P. macrops represents not fully grown specimens of P. glaber. 



Suborder Mysida 



Family MYSIDAE 



Subfamily Siriellinae 



SIRIELLA Dana 



SIRIELLA OCCIDENTALIS, n. sp. 



Text figs. 3 and 4 



Localities. — Serial numbers 310 B, 358 A, 406, 407 B. 



Description. — In his Siboga report Hansen (1910) divides the 

 species of Siriella into four groups. Using his grouping as a basis, 

 this species belongs to the second group, characterized as follows : End 

 of the telson with three small spines and a single pair of more lateral 

 long spines. Proximal joint of the exopod of the uropods with much 

 more than half of its outer margins furnished with spines, and at 

 least about twice as long as broad. Proximal widened part of the 

 telson with three pairs of marginal spines ; spines along the distal 

 third of the lateral margins of the telson closely set but irregular as 

 to length, as several long spines are found, and between each two of 

 these some, or near the end of the telson only two or one, smaller or 

 small spines are inserted. Both rami of fourth pair of male pleopods 

 terminating in very modified setae. Pseudobranchial rami of second 

 to fourth pairs of male pleopods spirally twisted. (Hansen, 1910.) 



Within this group the species may further be described as follows : 



Carapace somewhat produced but leaving the eyes and eyestalks 

 completely uncovered, frontal plate a broad, low triangle with the apex 

 slightly produced into an acute point. 



Eyes large and black. 



Antemml scale (text fig. 3a) extending forward as far as the 

 distal end of the antennular peduncle, three and one-fourth times as 

 long as broad, terminal lobe broader than long. 



