POURTALESLE. 



129 



in the number and size of the ambulacra! plates which go to make up 

 the sunken ambulacral 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. 18.3. Pourtalesia Jeffreym. 

 After Loven. 



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

 In P. Jeffreys!, 1 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. 



Fig 



185. Echixocbepis 

 setigera. 



Fig. 186. Spatagocystis 

 Challengebi. 



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

 groove is still more marked in Pourtalesia phiale W. Th., 2 while in Pourtalesia 

 laguncula 3 it has more the shape of that of P. Tanneri; that of P. hispida* 



1 Loven, Pourtalesia, PI. Ill, fig. 10. 



2 " Challenger " Echinoidea, Pis. XXII, fig. 1; XXII s , fig. 2. 



9 



3 Id. PI. XXII*, fig. 9. 

 * Id. PI. XXn», fig. 8. 



