NACOSP AT ANGUS GRACILIS. 



203 



Seen from above (PI. 98, fig. 3) a denuded specimen 17 mm. in length' 

 shows the broadly petaloid posterior ambulacra, the semipetaloid anterior 



^^i^. 



6.5 mm. 



Fig. 290. Nacospatangus gracilis. 



Yo. 



9 mm. 



Fig. 291. Nacospataxgus gracilis. 



pair with the anterior zone composed of simple pores and the simple 

 anterior ambulacrum. The uniform tuberculation of the coronal plates 

 is very marked, extending over the interporiferous zone of the lateral 

 ambulacra. 



11 mm. 



Fig 292. Nacospatangus gracilis. 



Va 



17 mm. 



Fig. 293. Nacospatangus gracilis. 



The great width of the posterior row of the posterior lateral ambulacra 

 is very striking, as well as the size of the anterior interambulacral plates 

 compared to those of the ambulacral zone. 



1 " Hassler " Echini, PI. IT, fig. 4. 



