102 



GEOLOGICAL BIOLOGY. 



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FIG. 16. FIG. 1 8. 



FlG. 15. Echinodermata, Crinoid. Taxocrtnus multibrachiatus Ly. and Cass. Carboniferous. 

 Above: calyx with stem. Below: the plates of the calyx dissected, st = stem, br free arms, air 

 = anal interradial plates ; rh = right posterior, Ih = left posterior, vr = anterior right, ?'/ = 

 anterior left, vu = anterior medial radial plates ; irk = right posterior, ilk = left posterior, 

 irv = right anterior, ilv = left anterior interradial plates ; z/", infrabasalia ; pb = parabasalia ; 

 fj^4 = radialia ; </I, d\\ distichalia, first and second rank ; br = brachialia ; a\-a^ = anal 

 plates ; *>,-/> 8 = larger interradial plates ; t smaller interradial plates ; ss, plane of sym- 

 metry. (After S. and D ) 



FlG. 16. Blastoid. Pentatremitidea Eifeliensis F. Ro. sp. Devonian, b = basalia ; r = 

 radialia ; p = ambulacra. (After S. and D.) 



FlG. 17. Cystoid. Caryocrinus ornatus Say. Silurian. A, calyx with stem s \ br = arms ; I, 

 II, III, first, second, and third zones of plates of the dorsal capsule ; / = porous plates ; i = 

 place of attachment of arms ; a = anal opening , view of the ventral dome, c = central 

 summit plates, i and a as above. C, inner surface of a plate of the second row, showing the 

 pores of the Hydrospires (/*) and their connecting canal (c). (After S. and D.) 



FlG. 18. Ophiuroid, A-H. Ophioceramis ferruginea Bohm. Jurassic. _ A, a complete 

 specimen, from under side ; br = arms. B the disk from the inner side ; bl = bursal 

 shields ; / = ambulacral pores. C ? mouth-skeleton from below; miu = mouth-angle; / = 

 papillae; me = angle-plates; ms = side shields; m = oral plates; b = second ventral plate. Z>, 

 disk from above; r = dorsal shield. E, a part of an arm from below; b = ventral shields; 

 s = lateral shields; / = ambulacral pores. F, a part of an arm from above; r and s as above; 

 st spines G, the same, lateral view. //, cross-section of an arm. /, Geocoma planata 

 Qu. sp.; bs = bursal slit; bl = bursal shield. (Steinmann and Doederlein.) 



