120 



PANAMIC DEEP SEA ECHINI. 



In Pourtalesia Tanneri (PI. 57, figs. 1, 5) there is a small labium, Fig. 109, 

 which is wanting in some specimens (Fig. 170) ; it is excluded from the 

 actinostome, and is separated from the large elongated hexagonal sternum 

 followed by two episternal plates, Fig. 171, by the anterior zone of the 

 posterior lateral interambulacra (PI. 56, fig. 7), and the second pair of plates 

 of the posterior lateral ambulacra (PI. 57, fig. 5), the first plates of which 

 reach the actinostome. 



4 l\\ L l - 



10 lulu 



Fig. 17-'. Pourtalesia Tanneri. 



16 mm. 

 Fni. 173. P. Tanneri. 



* 5a 



17 mm. 



Fig. 171. 

 Pourtalesia Tanneri. 



4 5a 



Fig. 174. P. Jeffrkysi. 

 After Lotem. 



The lateral posterior interambulacral primordials are diminutive, p. pi. 

 Figs. 172, 173 ; they do not reach the actinal system (PI. 57, figs. 1, 5), as 

 do the larger primordials of the anterior lateral interambulacra (PI. 57, fig. ■'<)■ 

 In P. Jeffrey®, the arrangement of the plates is somewhat different. 1 The 

 posterior interambulacral primordials are excluded from the actinostome, 

 the labium is actinal, Fig. 174, and is separated from the sternum by the 

 same set of plates, both ambulacral and interambulacral, as in P. Tanneri. 



In Spatagocystis, Fig. 175, the labium is separated from the sternum, 



1 Loven, Pourtalesia, PI. II. 



