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



inner angle of the orbital notch are two small sharp teeth arising from nearly the same 

 base, between which and the rostral tooth the anterior margin of the carapace is fringed 

 with long hairs, as it is also between the outer angle of the orbit and the latero- anterior 

 angle, which is directed obliquely forwards, curving outwards and upwards, the first 

 division or antennal region thins out into a marginal ridge, which is surmounted by a 

 series of six long outwardly and upwardly-curved teeth ; the second division which is 

 known as the hepatic region, is surmounted by five outwardly-directed and upwardly- 

 curved teeth, of which the anterior is the most prominent. Posterior to the cervical 

 suture the margin proceeds slightly outwards and then downwards, and is surmounted by 

 a series of seventeen teeth directed outwards, upwards, and forwards, except those on the 

 posterior margin, which are directed backwards and radiate in a curve corresponding 

 with the rest. The posterior margin bends in a manner corresponding with the form of 

 the animal, and supports a short curved spine near the articulation of the posterior margin 

 of the carapace with the first somite of the pleon, between which and the median line 

 on each side there are three or four small sharp teeth. 



The first somite of the pleon is longitudinally short, narrower than the second, and 

 supports one sharp tooth on the median line ; it has no coxal plate, the outer extremity 

 terminating in a nodular cusp that articulates with a corresponding cup in the carapace 

 (peltecleis) and locks it in position. 



The second somite is longitudinally longer than the first, and is bisected by a furrow 

 on each side of the median line, the central crest of which carries two sharp teeth, placed 

 one behind the other, the anterior of which is directed obliquely forwards, while the 

 posterior is nearly perpendicular ; the third, fourth, and fifth somites resemble the second 

 except that each gradually narrows in succession, and the coxal plates become more 

 pointed ; the sixth somite has no dorsal teeth, but protuberances only : the telson is 

 long and tapering, with two small longitudinal ridges on each side of the median fine. 



The ophthalmopoda (a) are small, obscure, and immovable, the upper portion is 

 bulbous and fills a small notch or cleft in the anterior margin of the dorsal surface of the 

 carapace, whence it narrows to a point and lies impacted in a hollow on the outer side 

 of both antennae (b, c), beneath the projecting antero-lateral angle of the carapace ; 

 a small tooth projects from the anterior surface of the upper or bulbous portion of the 

 ophthalmopod. It is impossible in the present condition of the animal to state with cer- 

 tainty, but from the appearance of the organ I am inclined to believe that vision existed 

 at two points, namely, at that part of the upper surface exposed within the orbital notch, 

 and inferiorly at the extremity of the ophthalmopod. The animal, however, can have 

 had only a very limited range of vision outwardly, by the aid of one lens above, and 

 another below and a little in advance, and even this, from the apparent density of the 

 cornea, must have been of a very imperfect character. 



The first pair of antennse (fig. c, b) has the first or coxal joint thick and bulbous on the 



