CRUSTACEA FROM THE 'CHALLENGER' EXPEDITION. 33 



long hairs which by far surpass it in length. In the larger species I could not examine 

 the first maxilla ; but it probably has got a palpus too. Lophogaster has not got it ; and 

 it is very interesting to find it in Gnathophausia, as it is one more connecting link between 

 this genus and Nebalia. The second maxillae, are large organs (fig. 6), covering the former 

 ones and exhibiting a flagellum, a two-jointed palpus, and an accessory eye. I tried 

 to make out the structure of this eye by hardening it and making it transparent, but did 

 not succeed ; all I saw was the cornea and a dark pigment inside. For him, however, 

 who has seen the same organ in the larger species, there is not the slightest doubt that 

 these sense-organs on the second maxillae are the same things which have been called 

 accessory eyes in the Euphausiidae. They are present in all the specimens of the genus 

 Gnathophausia in the same place. 



In the maxillipeds (fig. 7) of this species I could not find the palpus, which in the 

 larger is so clearly visible (fig. 16). Possibly it is wanting in the female ; for I do not 

 think that it escaped my attention as I looked for it with the microscope. 



The two gnathopoda (figs. 8 & 9) have got at their base breeding-lamellae and three 

 pairs of gills, one of which is situated on the ventral side^ while two are laterally covered 

 by the shield. No subjoints can be seen in these first two legs, traces of them are to be 

 found in the first and second pereiopods (figs. 10 & 11) ; but they are only very clearly 

 visible on the third and fourth (figs. 12 & 13). In the last (in which I have drawn the 

 breeding-lamella, fig. 14) they are wanting, as are also the gills at its base. Among 

 Mysidae we have the same thing which we find now in Lophogastridse, for these sub- 

 joints which are wanting in Siriella (as they here are in Lophogaster) are to be met with 

 in Mysis. 



The abdomen of Gn. zoea differs somewhat from that of the larger species. We do not 

 find here those squamiform prolongations, but have simply a few small spines at the 

 posterior and inferior angle of each segment. In the sixth we have the same peculiar 

 arrangement of its being divided by a deep ridge into two pseudo-segments which do not 

 articulate with each other. There is a spine bent backwards at the end of the first one, 

 and several small spines at the end of the second. 



The telson (8 millims. in length) terminates in a half-moon; the caudal appendages 

 are both jointed ; the pleopoda are very slender (fig. 15), and show a small tubercle at 

 the inner posterior side. 



The male differs from the female in this species by the length of the rostrum, which 

 in the former has one third of the length of the whole body, and in the latter only one 

 fifth. In the size of the inner antennae I see no great difference. Whether the male or 

 the female attains a larger size I cannot say ; the largest specimen of G. zoea which we 

 got was a female ; besides, it is very easy to tell a male from a female by the want of 

 breeding-lamellae in the former. 



3. Gnathophausia gracilis, n. sp. (PI. IX. fig. 1). 



Only one male of this smallest Gnathophausia-s-pecies has been hitherto got"; it came tip 

 on the 26th of August, in lat. 1° 22' N., long. 26° 36' W., 170 miles east of St. Paul's rocks, 

 from a depth of 1500 fathoms. It was on this same day that one of the specimens of Gn. 



SECOND SERIES. — ZOOLOGY, VOL. I. F 



