G4 THE VOYAGE OF H.M.S. CHALLENGER. 



Second pair of maxill;B with terminal joint verj- In-oad, exognatli comparatively small. 

 First pair of leg-s nearlj' similar in structure to maxillipeds and succeeding legs, save that 

 the terminal joint is somewhat expanded and armed with a fascicle of short spines. The 

 two last pairs of legs (piite ludimentary, being present only as minute, setiferous processes. 

 The four anterior jiairs of gills forming single, curved stems, fringed with a row of 

 narrow gill-sacs ; the three posterior pairs much more complex, sending oft' a branch 

 interiorlv; exterior l)ranch in last pair to a greater or less degree abundantly arliorescent. 

 The usual number of luminous globules present. 



Remarks. — This genus was established by Dana, who distinguished it from the genus 

 Thysanojwda, M.-Edw., chiefly by the rudimentary character of the two posterior pairs of 

 less. This, indeed, would seem to be one of the most striking features bv which the 

 present genus may be distinguished from other genera of Euphausiidaj. Moreover, the 

 structure of the sills is somewhat different from that in other forms of this famih*. 



The genus at present comprises no less than eleven different species, all of which are 

 represented in the Challenger collection. Of these, four only have been previously 

 recorded, the other seven being new. The Arctic species established by Kroyer under the 

 names of Tliysanopoda inermis, Thysanopoda neglecta, and TJiysanopoda longiccmdata, 

 which I previousl}' referred to the present genus, ought to be comprised within a distinct 

 genus, Boreopliatisia, G. 0. Sars, not represented in the Challenger collection. 



Since the genus Euphausia may be regarded as the t}^)e of the family, I have 

 deemed it advisable, before passing on to the special description of the species, to give 

 a general account of its organisation, as gathered frohi a careful dissection of several 

 specimens belonging to one of the species, Euphausia peUucida, Dana. 



General Description of the (j'enus. — The form of the liody (see PL XL figs. 1, 2 : 

 Pis. XIII.-XYI.) is generally rather slender, and somewhat compressed, ■^^-ith the tail 

 powerfully developed and always much longer than, sometimes even exceeding twice the 

 length of, the anterior division. 



All the integuments are very thin and translucent, admitting of the muscles of the body, 

 and also certain of the viscera, being more or less distinctly traceable through them. 



The carapace, as in other Euphausiidee, is comparativeh' small, leaving the bases of the 

 legs, with their gills, l)are, and posteriorly it does not completely cover the last segment 

 of the trunk, a portion of which always appears exposed above. Differing from all other 

 families of Schizopoda, it is, moreover, connate with the trunk along the whole of the 

 median line, in such a manner that none of the segments, excepting the last, appear 

 completely defined dorsally. Regarding its structure, it is very thin and pellucid, 

 without any kind of sculpture, save a slight transvei'se depression on its anterior part, 

 representing the cer\dcal sulcus. Posteriorly it exhibits in the middle a conspicuous 

 emargination, encompassing the exposed dorsal part of the last segment of the trunk. 

 The lateral wings of the carapace are evenly rounded, and project a, little over the sides 



