64 THE VOYAGE OF H.M.8. CHALLENGER. 



Second pair of maxillte with terminal joint very broad, exognath comparatively small. 

 First pair of legs nearly similar in structure td maxillipeds and succeeding legs, save that 

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

 two last pairs of legs quite rudimentary, being present only as minute, setiferous processes. 

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

 narrow gill-sacs ; the three posterior pairs much more complex, sending of!' a l)ran(-h 

 interiorly; exterior branch in last pair to a greater or less degree abundantly arborescent. 

 The usual number of luminous globules present. 



Memarks. — This genus was estaJilished by Dana, who distinguished it from the genus 

 Thysanopoda, M.-Edw., cluefl}' l»y the rudimentary character of the two posterior pairs of 

 legs. This, indeed, would seem to be one of the most striking features by which the 

 present genus may l)e distinguished from other genera of Euphausiidse. Moreover, the 

 structure of the gills is somewhat different from that in other forms of this family. 



The genus at present comprises no less than eleven differeut 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 Krciyer under the 

 names of TJiysanopoda inermis. Thysanopoda neglecta-, and Thysanopoda longicaudata, 

 which I previously referred to the present genus, ought to lie comprised within a distinct 

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



Since the genus Euphausia, may lie regarded as the t}"2:ie of the family, I have 

 deemed it advisalile, liefore passing on to the special description of the species, to give 

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

 specimens lielonging to one of the species, Eupjhausia jx'Uncida, Dana. 



General Description of the Genus. — The form of the body (see PI. XL tigs. 1,2; 

 Pis. XIII.-XA^I.) is generally rather .slender, and somewhat compressed, with the tail 

 powerfully de\eloped 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, l>eing more or less distinctly traceable through them. 



The carapace, as in other Euphausiida?, is comparatively small, leaving the bases of the 

 legs, with their gills, bare, and posteriorly it does not completely cover the last segment 

 of the trunk, a portion of wldch 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 i)ellucid, 

 without any kind of sculpture, save a slight transverse depression on its anterior part, 

 representing the cervical sulcus. Posteriorly it exhil)its 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 



