THYSAN'OPODA ( HISTATA. 209 



long. 115° 20' E. Probably all the specimens in the Copenhagen INIusoum were 

 taken at the surface of the sea during night. 



3. Tbysanopoda cristata G. O. Sars. 



Plate 3, figs. 4a^c; Plate 4, figs, la-lh. 



1883. Thysanopoda cristata G. O. Sars, Forh. Vid. Selsk. Christiania for 1883, no. 7, p. 22. 



1885. Thysanopoda cristala, G. O. Sars, Challenger Rept., 13, p. 104, pi. 18, figs. 15-20. 



1893. Thysanopoda biproducta Ortmann, Ergebn. der Plankton-Exped., 2, G. b. p. 8, taf. I, fig. 1. 



Sta. 4699. Dec. 25, 1904. Lat. 21° 39.5' S., long. 104° 29.8' W. 300 fms. to surface. 1 young .speci- 

 men. 



Sta. 4728. Jan. 19, 1905. Lat. 13° 47.5' S., long. 114° 21.6' VV. 300 fms. to surface. 1 adult male. 



Sta. 4736. Jan. 23, 1905. Lat. 19° 0.4' S,, long. 125° 5.4' \V. 300 fms. to surface. 1 immature 

 specimen. 



Description. — The frontal plate (Plate 3, fig. 4b) long, only a little broader 

 than long with the lateral margins considerably concave, strongly tapering 

 forwards and narrow in front, where it terminates in a moderately short, slender 

 rostrum which at its base is distinctly narrower than the end of the plate; in 

 the adult specimen (and in Sars's type) the rostrum seems to be articulated to 

 the end of the plate, but whether this is the normal state or is due to injury 

 I cannot decide. In the two much smaller specimens the rostrum is broader 

 at the base and not well-marked off. At the anterior end of the frontal plate 

 a very conspicuous, somewhat high, sharp dorsal keel is suddenly raised (Plate 3, 

 figs. 4a and 4c), the front end of which is even emarginate and terminates above 

 in a point; the keel goes backwards to near the iniddle of the carapace, and 

 about at the middle of its length, where the dorsal organ is found, it is rather 

 suddenly somewhat higher, while it is rounded downwards towards its posterior 

 end; in the smallest specimen the keel has no angle or incision at its front end, 

 and its anterior half decreases in height towards the rostrum where it disappears. 

 The carapace has no cer\'ical suture, but two obhque, moderately short impres- 

 sions on each side at a distance from the front lateral margin of about one third 

 of the length of the carapace ; the upper of these impressions is nearly horizontal, 

 the lower very oblique and below limited by a low narrow ridge. The lateral 

 part of the front margin of the carapace below the eye is produced in a triangular, 

 acute, somewhat small plate; at a considerable distance from the lower margin 

 a deep furrow is seen, beginning above the insertion of the maxilla and reaching 

 to near the hind margin of the carapace, where it bends upwards and terminates 

 at the middle of the side. A smaH tooth (omitted in fig. 4a by the engraver) 

 is found above the lateral margin — in the small specimen on the margin — of 

 the carapace somewhat before its posterior end; the tooth is acute, directed 

 outwards, forwards, and downwards. 



