POURTALESI^.. 



129 



ill the number and size of the ambulacral plates which go to make up 

 the sunken ambuhicral actinal grooves of these genera. Views of these 

 genera seen from the actinal side show the proportional extent which the 



Fig. 182. P. carinata. 



Fig. 183. Potrtalesia Jeffretsi. 



Afteb LovtN. 



actinal groove bears to the whole test, as well as their general outline. 

 In P. Jeffreysi^ Fig. 183, it occupies nearly one third the length of the 

 test, and is nearly half as broad as the test. In P. Tanneri (Pi. 56, fig. 1), 

 Fig. 184, it occupies about a fourth of the actinal side, flaring out laterally 



17 mm. 



Fig. 184. P. Tanneri. 



92 mm. 



Fig 185. Echinocrepis 

 setigera. 



Fig. 186. Spatagocystis 

 Challenoeri. 



and not having a re-entering curve as in P. Jeffreys. This form of actinal 

 groove is still more marked in Pourtalesia phialc W. Th.,- while in PourtaJesia 

 lagimcula^ it has more the shape of that of P. Tanneri; that of P. /iLyu'da* 



» Loven, Pourtalesia, PI. TIT, fig. 10. 



a " Challenger " Echinoidea, Pis. XXII, fig. 1; XXII», fig. 2, 



9 



» la. PI. XXII«, fig. 9. 

 * Id. PI. XXII*, fig. 8. 



