1274 THE VOYAGE OF H.M.S. CHALLENGER. 



than wide, and is followed by a terminal joint much narrower but immensely longer, 

 tapering so far as its initial narrowness permits, which may be regarded as the flagellum; 

 how diminutive are these lower antennas compared with the upper, may be judged from 

 the figures of both in the Plate, which are drawn to the same scale. In the male it is 

 probable that here, as in Scina borealis (Sars), the lower antennas attain a much greater 

 development; successive steps are seen in the figures a.i. B., a.i. C, and a.i. A., from 

 three different specimens ; the coalesced first and second joints of the peduncle are to 

 some extent free from the wall of the head and show a small blunt gland-cone ; the third 

 joint is rather longer than broad ; the fourth longer than the third ; the fifth longer 

 than the preceding two together, more or less bent except in the earliest stage ; the first 

 joint of the flagellum at first shorter than the last of the peduncle, then equal to it, and 

 eventually perhaps exceeding it in length ; this is succeeded in the different specimens by 

 three, four, and five joints respectively. In fig. a.i. C, these antennas are shown in their 

 position as folded back round the mouth organs. The flagellum-joints of specimen A were 

 seen to be microscopically scabrous near the convex margin, with little groups of spinules. 



Upper Lip unequally bilobed. 



Mandibles without palp, spine-row, or molar tubercle ; the trunk shallow, attached 

 along the straight upper border, the front terminating in a small cutting edge, which is 

 more or less triangular, striated in appearance, and minutely denticulate ; the secondary 

 plate of the left mandible is simdar to the principal plate, but rather smaller, the denticles 

 fewer, about fourteen in number. 



First Maxillse. — The inner plate appears to be rather broadly oval, distally hairy ; 

 the outer plate slender, a little curved, its outer margin convex, at some distance from 

 the apex interrupted and capped by a spine, the remainder of the plate being triangular, 

 with smooth outer margin, the inner carrying three denticles and a spine, the narrow 

 apex completely occupied by a spine ; the concave inner margin ends in a similar but 

 smaller triangular piece, with some minute denticles on either side and an apical spine ; 

 this plate therefore presents the very unusual feature of a cleft termination, and in some 

 positions the spine on the outer margin together with the two terminal triangles gives it a 

 tridentate appearance; 1 the palp, consisting of a single joint, is broader and a little longer 

 than the outer plate, its outer margin a little convex, the inner a little concave, with some 

 spinules adjacent, the distal margin nearly straight, with a spinule near the outer apex, 

 and a little tooth at the inner apex. The figure of these maxillas is taken from the South 

 Atlantic specimen, in which the principal apex of the outer plate shows five denticles. 



Second Maxillse. — The inner plate shorter and much narrower than the outer, 

 distally furred with numerous spines of various thicknesses but none large, the distal 

 margin narrow but truncate and having a blunt tooth on the inner corner ; the outer 

 plate rather broad, but not long, somewhat bent, furred with rather stronger spines than 



1 In Clydonia borealis G. 0. Sars describes this plate as " angusto, incurvato, indistincte tridentato." 



