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



on the former than on the latter, while more especially on the dorsal surface of the 

 second and third somites they are diminished in size, most probably from friction ; on the 

 anterior portion of the carapace they increase in size in a little ridge on the median line, 

 which is slightly represented posterior to the cervical fossa ; this ridge is anteriorly lost 

 in the rostrum, which is flattened and dorsally concave at the frontal margin, whence 

 it narrows laterally and becomes subcylindrical and then elevated into a compressed 

 rostrum (PI. XXI. c). Anteriorly the rostrum is armed with three strong teeth 

 above and six below ; a smooth space intervenes, more especially on the upper 

 surface, until posteriorly the margins diverge, when several strong teeth, of which the 

 second is the largest, and all are much larger than those on the general surface, con- 

 tinue in two subparallel conspicuous rows nearly to the cervical fossa. On the carapace 

 the spines or teeth point anteriorly, on the antero-lateral parts of the pleon they point 

 outwards and downwards, and on the rhipidura and posterior somites of the pleon 

 they point posteriorly. 



The eyes (c. a.a) are very small, not larger than the diameter of the small ophthal- 

 mopoda on which they are supported. They are situated immediately beneath the 

 rostrum, and have no orbit, although there is a depression on the upper surface of the 

 first pair of antennae similar to that which exists in those species in which the organ 

 of vision is well developed. 



The first pair of antennae (c, b) consists of three subequally long joints and two 

 short terminal flagella, which are subequal in length and a little longer than the peduncle ; 

 the inner flagellum is only very slightly stouter than the outer, and both are nearly free 

 from cilia ; the first joint of the peduncle is a little broader than the others, particularly 

 at its base, where a small flat tubercular process projects on the outer surface, near 

 which on the upper surface is a diagonal fissure, protected by cilia, that forms a passage 

 to the auditory chamber, which is lined with numerous short, robust, ciliated hairs 

 planted in rows, and contains a quantity of calcareous and silicious particles. 



The second pair of antennas (c, c) is large and robust at the base, and is implanted 

 a little below and outside the first pair. The coxa or first joint articulates freely 

 with the metope, and carries a short phymacerite directed obliquely inwards and 

 downwards, anterior to which is a short, stout-based, sharp-pointed tooth ; the second 

 joint is produced to a sharp point on the outer side, and supports a large scaphocerite 

 about one-third the length of the carapace, and has its outer margin slightly curved 

 outwards, stout, and fringed on the under surface with a dense row of inwardly-directed 

 short cilia ; the extremity is produced to a short tooth-like point from whence the 

 anterior and inner margins, fringed with long cilia, curve to the base ; the upper surface 

 is covered with short, sharp, anteriorly and obliquely directed spinules ; the under is 

 much smoother, but possesses more sparsely scattered spines ; the third joint is long, 

 dorsally and ventrally flattened, and fringed on the under side with a dense row of 



