POURTALESIA JEFFREYSI. 129 



variable, to judge from miranda and jeffreysi, the best known species, and the 

 pedicellariae, so well worked out by Mortensen, afford probably the most con- 

 stant characters. 



Key to the Species of Pourtalesia. 



Subanal rostrum large and conspicuous. 



Subanal rostrum with sides converging towards the rounded tip which is little or not 

 at all elevated. 



Width of test about .40 of length; posterior end of dorsal keel not overhang- 

 ing periproct; valves of rostrate pedicellariae relatively short and wide . . miranda. 

 Width of test about .50 of length; posterior end of dorsal keel overhangs peri- 

 proct more or less conspicuously; valves of rostrate pedicellariae longer and 



narrower jeffreysi. 



Subanal rostrum with sides nearly or quite parallel; tip truncate and more or less 

 markedly elevated in adults. 



Genital plates not completely fused together; size large (40-50 mm.); ophi- 



cephalous pedicellariae wanting; rostrate pedicellariae of two kinds . . . alcocki. 

 Genital plates completely fused; size not large. 



Size moderate (20-30 mm.); ophicephalous pedicellariae more or less 



abundant; rostrate rare or wanting laguncula. 



Size small (12-20 mm.); ophicephalous pedicellariae rare or wanting; 



rostrate more or less abundant tanneri. 



Subanal rostrum small, low, slightly tapering, its length much less than diameter of 



periproct; tridentate pedicellariae numerous and diversified hispida. 



Pourtalesia miranda. 



A. Agassiz, 1869. Bull. M. C. Z., 1, p. 272. 



It is greatly to be regretted that the original specimen on which this inter- 

 esting species was based is no longer to be found. Its fate is a mystery. As 

 already stated we have material in the M. C. Z. from Grenada collected by the 

 Blake, and the Ingolf secured many specimens in the northern Atlantic. It is 

 true that Mortensen questions whether the Blake material really is miranda 

 but Mr. Agassiz never doubted it and I do not think the differences between the 

 figures of miranda given in the Revision of the Echini and these Grenada speci- 

 mens are really important. They are partly due to inexact details in the figures 

 and are partly a matter of individual diversity. 



Pourtalesia jeffreysi. 



Wyville Thomson, 1872. Proc. Roy. Soc, 20, p. 496 (nomen nudum). 

 Wyville Thomson, 1874. Phil. Trans. Roy. Soc, 164, p. 747. 



Thomson gives a brief description of this northern species in his The Depths 

 of the Sea (1873) but it is quite inadequate for the identification of the species 



