^ BR. P. H. CAEPENTEB ON CEBTAI]^ POIjVTS 



IE' obviously belongs to the second cycle of plates (PI. I. fig. 1. 

 8), while the two IE" resting ujDon it (15, 16) are members of the 

 third cycle, the other four plates of which Grottsche also calls IE' 

 (11, 12, 14, 17). Alternating with them are the three plates 

 which Grottsche calls second radials (A, 13, 18). It appears to 

 me, however, that the symmetry o£ Semicosmites is hesamerous, 

 and not jjentamerous, as Grottsche and others have supposed ; 

 and I also believe the base to be dicyclic. The four plates of 

 the proximal series, called basals by Hall* and Grottsche, are 

 infrabasals (PI. I. fig. 1 ; ib, 1-4), two of them being double 

 plates, just as in the pentamerous Oodiacrinus, Sypocrimis, and 

 Sagenocrinus. The tripartite monocyclic base of Platycrinus and 

 the Blastoids is an analogous case. The six plates of the second 

 cycle (5-10), Hall's subradials, which alternate in position with 

 those of the first, are the basals (&). This basal ring supports a 

 series of nine plates, six of which (r) alternate with the basals, 

 and are, I believe, the radials ; while the other three (A, 13, 18) 

 which rest upon the three anterior basals are interradials {i). 

 Caryocrinus (PI. I. fig. 2) has only two of these (13, 18), the 

 median anterior one being unrepresented in that type. But in 

 other respects the lower part of its cup is entirely similar to that 

 of Semicosmites, and its hexamerous symmetry is even more 

 strongly marked. This is well shown by the fact that each of the 

 two large infrabasals (2, 3) is marked by two double rows of hydro- 

 spire-pores, which terminate respectively at the distal angles of 

 the plate, just as the median row on each of the two smaller infra- 

 basals terminates at its distal angle. There are thus six double 

 rows of pores, and at the distal angle of every iufrabasal the 

 double row gives rise to two other rows, one upon each of 

 the basals which rest upon it. It is true that these six basals 

 (5-10) are not all of the same shape or size ; but I do not see 

 how any one can doubt that they are all morj)hologically equiva- 

 lent, and belong to the same cycle of plates. Von Buch laid 

 great stress upon this point t : — 



•'Hier istkeine Spur, keine Audeutung, welche auf eine Zertheiluug zu Fiinf 

 hinfilhren konnte. AUes wird, bis zu den geringsten Kleinigkeiteu, von der 



* " Descriptions of some new Fossils from the jViagara Group," Twentieth 

 Annual Eeport New York State Cabinet of Natural History. Albany, 1867, 

 p. 315. 



t Ueber Cystideeu." Abhandi. d. k. Akad. d. Wiss. BerUn, 1S44, p. yj. 



