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



are dilated and shortly setiferous on their inner margins, the last lobe (or palp) elongated, 

 two-jointed, setiferous, and bearing at the apex three or four slender claws ; a branchial 

 plate attached to the base of the maxillse ; second paii' geniculated, three or four-jointed, 

 the basal joint produced into an angular setiferous lobe, the apical portion biarticulate, 

 slender, bearing numerous marginal setae, and three or four slender apical claws. Two 

 pairs of feet; first j)air elongated, slender, the two basal joints dilated, and bearing a 

 branchial lamina, the apical portion more slender, and having three or four long terminal 

 setae ; in the male this Hmb is larger, and has three long, equal terminal setse ; second 

 pair of feet rudimentary, two-jointed, and bearing two unequal apical setse. Post- 

 abdomen composed of two short, marginally-clawed flat laminse. 



Though closely related to the C3rpridinid8e, the Conchceciadee are clearly separated 

 from the former group by several well-marked characters. The remarkable organ found 

 between the anterior antennse, called by Dana "spiculum," by Sars "frontal tentacle," 

 is, perhaj)s, as regards function, an organ of touch. A structure agreeing with this in 

 general character is figured by Grube as occurring in Cypridina oblonga, but no other 

 author appears to have noticed anything similar amongst the Cypridinidse. In Grube's 

 figure two of these organs are shown, whereas in the Conchoeciad^ one only is present, 

 situated in the median line. The apparent duplication of the mandible by the abnormal 

 development of the basal joint of the palp is another very extraordinary family mark. 

 The second pair of feet is very small, so as readily to escape observation, and is indeed 

 left without notice by Dana, Lubbock, and Glaus. 



The animals belonging to this family appear to be generally of pelagic and natatory 

 habit, though Sars' specimens were obtained by dredging in depths of 200 to 300 fathoms. 

 They abound more especially in the tropical seas, few surface-net gatherings made in 

 those regions being without some rej)resentatives of the family of which Halocypris 

 atlantica, Lubbock, seems to be by far the most abundant and most widely distributed. 

 In the Challenger dredgings I have not recognised any trace whatever of their shells ; 

 this, together with a consideration of their structure, which specially fits them for a 

 natatory life, the females being (unlike those of the Cypridinidse) little less adapted for 

 this mode of existence than the males, leads me to believe their life on the sea bottom 

 to be an exceptional occurrence. Seeing the immense numbers of Halocypris which 

 evidently swarm in some parts of the ocean, one might perhaps expect to find their 

 empty shells in plenty at the bottom, but their subsidence in any great numbers would 

 probably be prevented by the abundance of predaceous animals, of whose food these 

 little creatures doubtless form an essential part, and by the excessive lightness and 

 delicacy of their shell-structure which would render subsidence so long a process as pro- 

 bably to ensure the solution or decomposition of the shell before its full accomplish- 

 nient. 



After a careful comparison of Dana's descriptions and drawings of the two genera, 



