76 BULLETIN 2 01, UNITED STATES NATIONAL MUSEUM 



two strong smooth spiniform setae set at a widely divergent angle 

 which is constant and characteristic in all the specimens I have ex- 

 amined. The exopod in S. pacifica bears two setae, one short and 

 simple, the other long and very curiously bent in an acute angle. In 

 JS. roosevelti there are also two setae, one quite short and simple, the 

 other longer and more robust and not bent in the same way as in 

 S. paciftca. 



The most easily observed character for distinguishing the females 

 of the two species is the number and spacing of the spines on the 

 outer margins of the proximal joint of the outer uropods. In S. 

 pacifica there are 14 or 15 spines, rather closely set, whereas in S. 

 roosevelti there are only 8 or 9 spines somewhat distantly spaced so 

 that, although fewer in number, they occupy about as much of the 

 margin as they do in S. pacifica. 



S. pacifica and S. roosevelti agree with each other and differ from 

 all other species of the genus with the exception of JS. anomala Hansen, 

 in having both rami of both the third and fourth pleopods of the male 

 terminating in modified setae. They can both be distinguished from 

 S. anomala by the antennal scale, which in the latter species is of very 

 special and peculiar shape in the male. 



Occurrence. — Galapagos Islands: The Albatross expedition of 

 1887-89 collected two lots: Chatham Island, April 4 and 14, 1888, 

 several thousand specimens; Albemarle Island, April 10, 1888, 3 

 specimens ; from the Presidential cruise of 1938 there is the material 

 upon which I reported in 1941. 



Distribution. — This species is known only from the waters of the 

 Galapagos Islands, where it would appear to be very abundant. 



SIRIELLA PANAMENSIS, new species 



Figure 20 



Description. — This new species is very closely allied to the other 

 American species, S. pacifica, S. roosevelti, and S. chierchiae, and 

 females are almost impossible to distinguish from those of the other 

 three species. The males, on the other hand, are readily separated by 

 the form of the modified setae on the third and fourth pleopods. The 

 species belongs to the second group of Hansen's classification, for the 

 definition of which see under S. chierchiae, and within this group may 

 be further defined as follows : 



Carapace somewhat produced but leaving the eyes and eye stalks 

 completely uncovered, similar in both sexes, rostral plate a short tri- 

 angle with an acute point, not extending forward beyond the base of 

 the eye stalks. 



Eyes of moderate size, pigment black. 



