30 DISCOVERY REPORTS 



2-4 teeth, and (ii) with the anterior margin of the rostral plate smooth, the antero-lateral angles rounded 

 (in Fage's description minutely serrulated) and with the outer margin of the antennal scale armed 

 with 9-12 serrations. It may be that these two groups do represent two separate species, but Tattersall 

 (1951) put forward the interesting suggestion that the differences between the groups might be sexual. 

 He noted that the Challenger specimen was a female and that all the specimens examined by Hansen 

 and Fage were male. All his own specimens were too immature for their sex to be ascertained, so that 

 he was unable to obtain any evidence from them. Unfortunately both the Discovery specimens are 

 female, but it is significant that they agree with the Challenger specimen, which was also a female. 

 The eyes in this species are very long and slender, nearly four times as long as broad. The cornea is 

 no wider than the eyestalk and occupies about one-fourth of the whole organ. There is a well-marked 

 finger-like ocular papilla on the distal inner margin of the eyestalk. Hansen figured a papilla in this 

 position but made no mention of it in the text (Fig. 1 B). The labrum is flask-shaped and quite 

 symmetrical, with its anterior end produced forward into a long acute process (Fig. 1 C). 



Distribution. Chalaspidum alatum is known to have a very wide distribution in the deep waters of 

 the Pacific. Since the type was taken in the Indian Ocean, off Kerguelen Island it has been recorded 

 from four stations in the East Pacific, off the west coast of Peru (Hansen, 191 2), from the China Sea, 

 north of New Guinea and from the Gulf of Panama (Fage, 1939, 1941) and from two stations to the 

 south of Japan and one to the west of San Diego, California (Tattersall, 195 1). Its occurrence in the 

 South Atlantic considerably extends its known geographical range. The record of the type simply gives 

 the depth as 1800 fm. and it is not stated whether a closing net was used. Hansen's specimens were 

 taken in vertical hauls of 300 and 400 fm. to the surface. The records of the ' Dana ', giving the length 

 of the cable out and the depth of water over which it was fishing, indicate that the animals were 

 living between depths of 300 m. and 2500 m. The capture of an immature female in a closing net fishing 

 between 2400 m. and 2500 m. at Discovery station 101, and of an adult in a net fishing between 

 1050 m. and 1000 m. at Discovery station 253 proves that the species can live at great depths. The 

 robust abdomen and the strongly developed pleopods suggest that it is a powerful swimmer and that 

 in all probability its vertical range is considerable. 



Genus Gnathophausia W.-Suhm, 1873 



1873 Gnathophansia (lapsus calami) W.-Suhm, p. 400. 



1874 Gnathophausia, Humbert, p. 206. 



Remarks. The genus Gnathophausia very closely resembles the fossil genus Tellocaris (Peach, 1908, 

 p. 9) as regards the telson, but even more closely in the form and armature of the carapace with its 

 anterior margin serrated and produced into a long dentate rostrum and the posterior margin produced 

 into a long median dorsal spine which is also frequently dentate. This spine is always present in young 

 specimens and usually persists as a long projection, but in some species it becomes progressively shorter 

 as the animals approach maturity and in large specimens may almost disappear. 



The chief generic characters are the tough, parchment-like integument ; the large, shield-like cara- 

 pace adorned with strong raised keels which are often toothed; rostrum long and sharp with three 

 longitudinal, dentate ridges making it triangular in section ; posterior margin of carapace produced 

 into a strong median spine; pleural plates of abdominal somites bilobed; eyes with well-developed 

 papilla; sixth abdominal somite with well-marked groove running around its median region; maxillule 

 with a two-segmented, setose, backwardly reflexed endopod ; first thoracic exopod absent or reduced 

 to a small unsegmented plate; exopod of uropod broad, two-segmented, outer margin of proximal seg- 

 ment naked and terminated by a strong spine ; telson entire with a strong constriction near the apex 

 which is armed with two very strong curved spines which together form a backwardly directed crescent. 



