204 



PANAMIC DEEP SEA ECHINI. 



A profile view^ as well as a view from the abactinal side (PI. 98, figs. ^, ^) 

 shows the abrupt passage, near the ambitus, of the small tubercles of 

 the abactinal part of the test to the large tuberculation of the second pair 

 of plates of the interambulacral areas (PI. 98, fig. 2). This is also shown 

 in PI. 98, figs. 8-11, where the large tubercles are arranged in rows parallel 

 to the ambital suture of the second posterior plate of the right posterior 



lateral interambulacrum. The specimens 

 figured on PI. 98, figs. 8-lJ, range in size 

 from 6.5 to 17 mm. 



Among the Spatangoids we find a great 

 diversity in the arrangement of the primary 

 and secondary tubercles in the large inter- 

 ambulacral plates of the actinal side. This 

 leads to most characteristic patterns which 

 have not as yet been used either for generic 

 or specific characters. A comparison of the 

 patterns of some of these actinal plates, Figs. 

 257, 290-294, shows in a striking way how 

 important these characters are among the 

 Spatangoids. The earliest indications of 

 such designs are found among the Cassidulidse. The patterns take their 

 greatest development among such forms as Metalia, Lovenia, Maretia, 

 Rhynobrissus, and are in striking contrast with the simple patterns of 

 Brissus, Meoma, Brissopsis, Echinocardium, and others. 



On the actinal plastron the tuberculation is coarse towards the labium, 

 and quite small and crowded towards the subanal plastron. On the actinal 

 surface, the ambulacral zones, composed of large plates, are broad and bare 

 as well as the adjoining edges of the interambulacral areas, forming a 

 striking contrast to the narrow ambulacral zones of the abactinal surface 

 with their small and diminutive plates. 



The actinostome is somewhat pentagonal, with the actinal edge of the 

 labium slightly raised. 



A young specimen of only 6.5 mm. in length (PI. 98, fig. l) seen from the 

 actinal side does not show any marked differences from older specimens. 

 The abactinal system of a specimen of 6.5 mm. (PI. 98, fig. 5) has only 

 three genital plates, no genital pores, Fig. 296, and a few madreporic 



» " Hassler" Echini, PI. II, figs. 3, 5. 



Fig. 294. 



no mm. 

 LiNOPNEUSTES LONGLSPINUS. 



