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and oblique posteriorly ; the ischium shoit, articulating with the pos- 

 terior margin of coxa near the center, and opposite the angle formed by 

 the posterior oblique margin ; the remaining joints about one-third the 

 length of the coxa; the first joint following the ischium longer than the 

 Three terminal ones; the inferior margin produced anteriorly ; all finely 

 serrated on the posterior margin. Of the fifth pair the coxa only 

 developed; membranous, broad, about one-third the length of the coxa 

 of the fourth pair. Abdomen narrower than the thorax ; segments grad- 

 ually decreasing in breadth posteriorly ; longer than the thoracic seg- 

 ments. Posterior abdominal appendages foliaceous, biramous; the 

 details of their structure similar to those of P. rissoinw. Telson broadly 

 triangular, apex obtuse. 



Length, .12 of an inch. 



Locality : North Pacific Ocean. Latitude 21° north ; longitude 151° 

 west. Collected May 20, 1873. 



This species is closely related to P. rissoinw; the differences are chiefly 

 in the structure of the guathopoda, and of the third and fourth pairs of 

 thoracic feet. The gnathopoda bear a striking resemblance to those of 

 the young of P. serratus, but as the rest of the structure of the animal 

 shows no evidence of immature development, this is undoubtedly their 

 normal adult condition. 



I dedicate the species to the eminent English carcinologist, C. Spence 

 Bate, who, more than any other writer on the subject, has helped to elu- 

 cidate this order of Crustacea. 



AMPHIPEONOE SERE UL ATA, n. sp. 



Head rounded ; superior surface slightly convex, longer than the infe- 

 rior surface; antero-inferior angle obliquely rounded, less projecting than 

 the antero superior ; front hollowed ; eyes diffused, covering the greater 

 portion of the lateral surfaces of the head. Superior antennte short, 

 peduncle three-joiuted ; the third joint large, slightly produced antero- 

 inferiorly ; inferior surface convex, and densely covered with long hairs; 

 flagellum articulating with superior margin of third joint subapically, 

 triarticulate, having at the apex of each articulus two or more long 

 auditory cilia. Inferior antennse five-jointed, folded four times, and con- 

 cealed beneath the head ; first three joints subequal ; fourth about two- 

 thirds the length of the preceding; fifth very short; margins of all the 

 joints shortly ciliate. The three anterior segments of the thorax nar- 

 rower than the following ; the four posterior subequal, gradually in- 



