OBINOIDS. 157 



shows a marked tendency to differentiate along the radial lines, 

 assuming most wonderful phases, which culminated in Telio- 

 crinus, Strotocrinus and Steganocrinus. The more primitive 

 forms of Actinocrinus have the free arms, as they leave the 

 calyx, nearly at equal distances from one another; though in 

 certain species the arms begin to show traces of separation 

 from those of the adjoining rays. Interradial plates still 

 further increase the distance between the clustered free-arm 

 bases of the several rays, until finally the calyx has become 

 strongly quinquelobate. The first section gradually diminished 

 in numbers, and disappeared in the upper part of the Burling- 

 ton; but the second continually grows more and more promi- 

 nent, and ultimately attains huge dimensions before the extinc- 

 tion of the group. 



In the upper portion of the Burlington appears a small 

 group of crinoids — Teliocrinus — possessing all the characters 

 of Actinocrinus, except that the lower brachials, for some dis- 

 tance have become larger and appear like calyx plates. These 

 are all firmly anchylosed, and do not give off the free, biserial 

 arms until the fifth or sixth order of brachials. The calyx thus 

 possesses a more or less well defined lateral extension, passing 

 around above the brachials of the second order. This has led 

 to the union of this group with Strotocrinus ; but the rim, 

 though very striking and very similar in each, seems to be a 

 separate development in the two genera, rather than different 

 stages of the same feature. In the ornamentation, the ventral 

 structure, and the possession of a very long anal tube, the af- 

 finities of Teliocrinus are manifestly much nearer the typical 

 representative of the family than Strotocrinus. 



The Physetocrinus type begins to make its appearance in 

 the Kinderhook, as a derivative of Actinocrinus. The earliest 

 known divergence, perhaps, is shown best in A. ornatissinius 

 W. & Spr. from the lowest member of the Lower Carboniferous. 

 In this form the radial portions of the calyx have commenced 

 already to become somewhat lobate, and the arms to grow 

 longer and more slender. The plates of the ventral side are 

 all quite small, the orals indistinguishable from the surrounding 



