II. The Order EUPHAUSIACEA. 



This order comprises in all 10 genera hitherto established, 6 of vvhich are represented 

 in the "Siboga" collection. In this paper I establish a single new genus, Psaideicpkausia, on a 

 species already described in the "Challenger" Report as Eiiphausia laüfrons G. O. Sars. As 

 already stated, the "Siboga" captured 25 species, 7 of which are described here as new, while 

 an eighth species, Etipliausia Siöogce, has been briefly characterized by me in a note on some 

 pelagic Malacostraca secured at Amboina by M. Bedot and C. Pictet. 



The investigation of the "Siboga" collection to<jether with material from other Oceans 

 has afforded some results which may be stated here as introductory remarks. 



The antennulae, especially the equipment of their peduncular joints with lobes, tubercles, 

 keels or spines and the exact shape of such protuberances, ought to be studied more thoroughly 

 than generally has been the case in the literature; in the large genera Thysanopoda M.-Edw. 

 and Eiipliausia Dana even minor details are frequently much more important than generally 

 believed. In all species of Nematoscclis G. O. Sars and Stylocliciron G. O. Sars the two distal 

 joints of the antennular peduncles are much or very much thicker, and especially the third joint 

 is besides conspicuously shorter, in the male than in the female ; in Stylochciron the fiagella show 

 interesting sexual and specific differences. In all genera the distal end of the first peduncular 

 joint of each antennula possesses above on the inner side a short row of setse which project 

 forwards and terminate as hooks ; by these hooks, which catch those from the antennula opposite, 

 both antennulae are coupled together. 



The preanal process or spine on the lower side of sixth abdominal segment has been 

 described by various authors as affording specific differences. But it seems to have been over- 

 looked that this process in most cases shows sexual difference, being in most genera simple and 

 often small in the male, while in the female it is most frequently broader, compressed, serrated 

 or with two, three or several spines in a longitudinal row and decreasing in size backwards. 

 The process may exhibit great difference in females belonging to different genera, but it seems 

 to be as a rule without value for separating allied forms of the same genus. 



On p. 1 I have already dravvn attention to the extreme importance of the copulatory 

 organs on the first pair of male pleopods. Here a description of these organs in the genera 

 represented in the "Siboga" collection may be given. As the male of Benthcuphmisia G. O. Sars 

 is unknown to me, the genus Thysanopoda M.-Edw. is taken as the type, for which it is well 

 qualified, as all the constituting elements of the organ are excellently developed. 



