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



arc the young of this species ; the uncertainty must be borne in mind in considering the 

 following facts. These specimens are immature, as is shown by the non-development of 

 the terminal segment of the thorax; the most remarkable peculiarity about them is the 

 great length of the lateral prolongations of the caudal shield ; these far exceed in length 

 the same process of the adult Eurycope novse-zelandise, and in fact resemble the present 

 species and Eurycope atlantica, from the former of which these young examples show no 

 very great differences. Fig. 2 of PI. IX. illustrates the external characters of these 

 young specimens. If they are really the young of Eurycope novse-zelandise, the fact will 

 be of interest as tending to show that this species has been derived from a species nearly 

 identical with Eurycope fragilis. This will be some evidence in favour of regarding 

 Eurycope fragilis as a (comparatively speaking) archaic form, and its very wide distribu- 

 tion, which will be referred to presently, is quite reconcilable with this view. 



Station 147, off Marion Island, December 30, 1873 ; lat. 46° 16' S., long. 48° 27' E. ; 

 depth, 1600 fathoms ; bottom temperature, 34° '2 F. ; Diatom ooze. 



Station 152, Southern Ocean, February 11, 1874; lat. 60° 52' S., long. 80° 20' E. ; 

 depth, 1260 fathoms ; Diatom ooze. 



Station 158, Southern Ocean, March 7, 1874 ; lat. 50° 1' S., long. 123° 4' E. ; depth. 

 1800 fathoms ; bottom temperature, 33°'5 F. ; Globigerina ooze. 



Station 237, off Yokohama, June 17, 1875; lat, 34° 37' N., long. 140° 32' E. ; 

 depth, 1875 fathoms ; bottom temperature, 35 0, 3 F. ; blue mud. 



Eurycope atlantica, F. E. Beddard (PL IX. fig. 13). 



Eurycope atlantica, F. E. Beddard, Proc. Znnl. Soc. Lond., 18s5, pfe iv. p. 919. 



This species is represented by a single specimen, which was dredged in the North 

 Atlantic, from a depth of 900 fathoms. 



Eurycope atlantica is very similar to Eurycope fragilis; as, however, all the 

 individuals of the latter species agree to differ from the present in a number of small 

 though perfectly constant characters, the separation of the two forms appears to be 

 necessary ; the main points of difference are as follows : — 



In Eurycope atlantica there are two spines on the head, placed on either side of the dorsal 

 median line, and two curved spines, placed one behind the other, upon the caudal shield. 



In Eurycope fragilis there are no spines upon the head, and only one spine upon the 

 caudal shield, situated not upon the caudal shield itself, but just anterior to it in a 

 region which I imagine to correspond to the anterior abdominal segment. Moreover, 

 the shape of the caudal shield is distinctly different in the two species. 



The example of Eurycope atlantica only measures 10 mm. in length; the body i> 

 rather narrower, but of fairly uniform width ; it does not narrow greatly either at the 

 anterior or at the posterior extremity. 



