CRUSTACEA FROM THE ' CHALLENGER ' EXPEDITION. 41 



Chalaraspis were the only representatives of the order, from which only in later periods 

 of the earth the well-known shallow-water members of the Schizopod families have 

 developed. 



I have called the animal which I shall now describe JPetalophthalmus, and the species 

 P. armiger. The first specimen, a female, was caught by the trawl in lat. 2° 25' N., 

 long. 20° 1' W., about midway between Cape Palmas and St. Paul's Rocks, from a depth 

 of 2500 fathoms. "We afterwards got a male in lat. 1° 22' N., long. 26° 36' "W., about 

 170 miles east of St. Paul's Rocks, from 1500 fathoms, and, finally, a female in lat. 

 35° 41' S., long. 20° 55' W., from 100 fathoms, about 400 miles west of Inaccessible Island 

 (Tristan d'Acunha group). The male has a length of 37 millims., the largest female of 

 44 millims., and the smaller one of 30 millims. . 



The carapace, soft and parchment-like, is in no connexion with five posterior segments 

 of the body. In the female, where it has not quite one half of the total length of the 

 animal (it is 18 millims. in length in a specimen of 44 millims.), it covers in its ordinary 

 position nearly all the segments of the pereion. It has a small rostrum (fig. 1), \rhich 

 is very little prominent, a small spine at its anterior border underneath the eye, and 

 sharpened anterior angles. The posterior and inferior angles are rounded ; and the sur- 

 face of the whole carapace is perfectly smooth. A slight transverse sulcus divides it into 

 an anterior and a posterior portion, the latter of which is by far the largest. 



Underneath the rostrum are the eye-stalks, terminated by concave spherical plates 

 having a diameter of 3 millims. ; they are simply a duplicature of chitinous matter. On 

 examining them under the microscope I could not find a trace of any eye-like structure. 



The first antennse have a three-jointed funiculus (I consider the small joint in fig. 3, 

 which is not to be seen in the first antenna of the male, to be not a fourth, but an ex- 

 ternal pseudo-joint) and two flagella, the external of which is enlarged at its base and 

 covered with hairs at the inner side. 



On the second antenna (fig. 4) there is a lamellar appendage (fig. 5) which has no 

 spines. 



The labrum is subcordiform (fig. 6). The mandibular (fig. 7) have a very strong 

 manducatory portion, with many denticulations and stiff hairs. The second joint of their 

 palpus is enlarged ; the third has a rounded point and many strong hairs at its inner side. 

 The under lip is somewhat like that of Chalaraspis, and bordered anteriorly with small 

 hairs. I could not draw it, as I saw only a part of it, the organ being broken when I 

 tried to take it out. 



The first maxilla? have two processes, showing many hairs and a strong denticulation 

 (fig. 8) ; they have no palpus. The second maxillae (fig. 9) have both palpus (p) and fla- 

 gellum (fl). The maxilliped (fig. 10) has a much more perfect palpus, quite close to its 

 fiagellum, than Gnathophausia has ; besides, there is at the inner side of the third joint 

 one of those fiat lamellar appendages which are known in the maxilliped and first gna- 

 thopod of Mysis and Siriella, and which in the male of our genus are indeed present 

 on both appendages, in the female, however, only on the maxilliped. 



The first gnatlwpod (fig. 11) has still maxillipedal functions, though it is rather elon- 

 gated ; its penultimate joint, however, is enlarged and recurved, and terminated by a 



SECOND SERIES. — ZOOLOGT, VOL. I. G 



