16 STRUCTURE OF THE CYSTIDEiE. 



In the genus GhjptosphcBrites (Miiller), represented by the species 

 Sphceronites Leuchtenbergii (Volborth), very slightly impressed grooves 

 radiate from the ambulacral orifice and ramify over the surface of 

 the body. At the end of each branch the place of the attachment of 

 a pinnula is seen. Upon the closest examination of good specimens 

 I have been unable to detect any indication that these grooves were 

 occupied by an arm that w^as bent backward upon the body as in the 

 genera Apiocystites (Forbes), and Callocystites (Hall). It is also quite 

 clear that the pinnulae were not seated upon arms of this kind, but 

 immediately upon the surface of the plate. The grooves are not 

 excavated but impressed ; they appear as if they had been formed by 

 several fine threads lying on the surface, while the plates were too 

 soft to sustain their weight. In this species the pinnulse were distant 

 from each other and scattered over the greater part of the body. In 

 C. cerasus they formed a circle around and quite close to the orifice, 

 and in E. aiigidosus they were also confined to the apex, but some- 

 what scattered According to my views we have in these forms the 

 lowest and most rudimentary condition of the radii yet seen in any 

 Crinoideae or Cystidese. The ambulacral vessels issued from the 

 interior through the orifice, and having nothing to support them, 

 crept along the surface, sending out branches to those points where 

 the pinnulas arose. The main trunk of the arm, or that which 

 bears the pinnulae in the Crinoids, was totally absent : it was never 

 developed. There is nothing but the grooves and the pinnulae to 

 indicate the existence of an ambulacral system. 



2. Cystideae in which the arms were developed, but bent back- 

 ward and attached to the body. In these we perceive a structure 

 one stage more perfect than in the several species just noticed. The 

 arms of Apiocystites pentrematoides (Forbes), Callocystites Jewettii (Hall), 

 and Glyplocystites multiporus, are all constructed upon the same type. 

 They originate in tlie apex of the fossil, where their bases are all 

 crowded together into a narrow space, in the centre of which is the 

 ambulacral orifice. They are composed of double series of flat plates 

 which alternate with each other, and have the usual grooves of the 

 Crinoids along their centres. On each side of the groove is a row of 

 pinnulae. From the main groove smaller ones branch out to the 

 base of each pinnula. The whole structure is exactly that of the 

 arms of the true Crinoideae, but not so perfectly developed. The 

 arms of all the Crinoids have sufficient strength to stand erect, but in 

 these Cystideag it appears to have been otherwise, and consequently 

 we find them not free and supporting themselves, but lying at full 



