AGASSIZIA EXCENTUICA. 7:; 



aus, Astropyga, and other Diadematidse and Echinothurioe ; in the last, there 

 is, as I bave shown, even what we mighl consider in some cases a regular 

 marginal fasciole, as in Phormosoma. The miliary granulation of the Cly- 

 peastroids generally, and the comparatively small radioles the) carry, maj 

 according to this view be considered as embryonic features which have 

 become greatly specialized, the whole test retaining the granular tubercula- 

 tion characteristic of the earlier Crinoids, with bul slight modifications in the 

 fasciolar radioles covering the whole test, if I may ><> call them, while they 

 become, strictly speaking, minute primary or secondary radioles. 



Although in the young stages of such Spatangoids as Bemiaster, Bris- 

 sopsis, Schizaster, and the like, the fascioles make their appearance verj 

 early, yet in this youngesl stage of Agassizia there is at a corresponding 

 period no well-defined fasciole band, ami it is only in a somewhat more 

 advanced stage (4 mm. long, diam.) thai we get a clearly defined fasciole. 

 This seems to affect the character of the spines round above and below it. 

 and Ave have in the stage just mentioned a well-defined lateral marginal 

 fasciole close to the ambitus. This fasciole is in reality only an extension of 

 the subanal fasciole, such as we find a remnant of in Argopatagus. The 

 peripetalous fasciole is also developed, and its anterior extremity come- dow n 

 close to the ambitus, a- it does in Paleopneustes. 



In the youngest Agassizia i •'! mm. long, diam.) there are three or four 

 single pores forming the rudimentary petals of the lateral ambulacra, The 



apical system is represented in this stage inereh by the large madreporic 



body which covers the whole apex. The surface of the test in these younger 

 stages, more especially in the ambulacra! areas, is covered ly numerous 

 small-headed, short-stemmed pedicellarise ami ly minute straight miliary 

 spines, often club-shaped. 



In a specimen measuring H mm. in longitudinal diameter, the odd ante- 

 rior ambulacrum was not yet developed at all: the lateral ambulacra con- 

 sisted of six and seven pores, the anterior ambulacra being composed oi 

 single rows of pores, the posterior ambulacra of double tow-: the anterior 

 rows di the posterior ambulacra were made up of three small pairs of pores 

 wiih a couple of single pores near the apex of the ambulacrum. 



Mcoma ventricosa Li re. 



Florida Bank, an. I ..(r It 



