CHAP. IV.] 



THE VOYAGE HOME. 



193 



nearly of an age. In P. eplnpp^fer the marsupiuni occupies 

 the greater part of the dorsal surface, and its passages run close 

 up to the edge of the mouth, so that the eggs pass into them at 

 once from the ovarial opening without exposure. 



In the male there is, of course, no regular marsupium ; but 

 the plates are arranged in the middle of the back somewhat as 

 they are in the female, except that they are not raised upon 

 peduncles; so that it is not easy at 

 once to distinguish a male from an 

 infecund female. 



Although we have taken species 

 of Psolus sometimes in great abun- 

 dance in various parts of the world, 

 particularly in high latitudes, south- 

 ern and northern, I have never ob- 

 served this peculiar form of the re- 

 productive process except on this one 

 occasion. 



On the 28th of January we dredged 

 from the steam pinnace in about 10 

 fathoms water off Cape Pembroke, at 

 the entrance of Stanley Harbor, a 

 number of specimens of a pretty lit- 

 tle regular sea-urchin Goniocidaris 

 Ganallculata^ A. Agassiz. 



The genus Goniocidaris (Desor) 



seems to differ from the genus Ci- 



FiG. 40. — Psohts ephippi/er, s(ime of 

 the Plates of the Maisnpiiim re- 

 moved. Three times the uatural 

 size. 



daris- in little else than in having a 



very marked, naked, zigzag, vertical 



groove between the two rows of plates of each inter -am- 



bulacral area, and one somewhat less distinct between the 



ranges of ambulacral plates. It includes about half a dozen 



species, which appear to be mainly confined to the colder 



regions of the southern hemisphere, although two of the spe- 



