138 FOSSIL CRINOIDS. 



= Cyathocrinoidea of Bather, plus Dendrocrinus and most of its 

 allies, and Botryocrinus and its allies. 

 Also the Non-typical Camerata ( = Adunata of Bather) . 

 Geological range. Ordovician to Middle of Lower Carboniferous; with a 

 feeble reminiscence in Lecythiocrinus of the Upper Coal Measures, and perhaps 

 in Guettardicrinus and Hyocrinus, and in exceptional cases among the Recent 

 Crinoids. 



4. A close, immovable suture, with all articular structures completely 

 obliterated, the rays being rigidly incorporated into the calyx by the growth 

 of solid supplementary plates: A still more highly specialized derivation from 

 No. 1. Example in fossils, Actinocrinus. 



The Typical Camerata. 



Geological range. Limited to the Palaeozoic. 



Referring now only to the dicyclic Inadunata, it will be seen that plan No. 1, 

 represents the Poteriocrinidae of Wachsmuth and Springer, including the 

 genus Poteriocrinus as a modification in the direction of No. 3, which did not 

 completely attain the senile condition. While it presumably existed from 

 the earliest times, we have not the specimens to demonstrate it clearly for the 

 Ordovician and Silurian. Cupulocrinus has wide, straight facets, but may have 

 the articulation of No. 2, as it has other tendencies towards the Flexibilia. 

 Merocrinus also has wide facets, but the known specimens do not show how the 

 joint faces are. In fact this plan was for the time completely overshadowed 

 by the specializations of the other three, which held the field with diminishing 

 preponderance while they ran their respective courses to extinction, — Nos. 2 

 and 4 within the Palaeozoic, and No. 3 practically so. As the others diminished, 

 No. 1 became vigorous, as the dominant plan of the later Palaeozoic, and con- 

 tinued to the present day. 



Plan No. 3 represents substantially the Cyathocrinidae of Wachsmuth and 

 Springer, with their usually narrow, horseshoe facets; it appeared in the earliest 

 Ordovician, parallel with those of the Camerata and the Flexibilia; and it ended, 

 as a morphological character of any importance, much before the close of the 

 Palaeozoic. The latest strong genus in which it is known is Barycrinus, in the 

 Warsaw; it reappeared in Lecythiocrinus, a rare and exceptional form of the 

 Upper Coal Measures; perhaps in Hypocrinus, which is little known, even its 

 exact horizon; and in the Mesozoic Guettardicrinus, and the Recent Hyocrinus; 

 it also tends to appear exceptionally among the Comatulids. 



In order to bring the facts of geological succession more clearly before us, 



