24 SMITHSONIAN INSTITUTION 



MORPHOLOGY 



As already stated, knowledge of the crinoids included in the group Flexi- 

 bilia is of much later date than that of the other major divisions. The first 

 illustration in the literature of a specimen belonging to this group is a figure 

 of Ichthyocrinus pyriformis published by Ellis * in 1762, without name, in con- 

 nection with an account of a Recent stalked crinoid from Barbados; this was 

 afterward refigured by Parkinson 2 in 1808 under the name of the " Fig Pen- 

 tacrinite. " The next was that of a specimen of Amphicrinus scoticus figured 

 by David Ure 3 in 1793, under the name of Encrinus. The first species to be 

 named was J. S. Miller's Cyathocrinus tuberculatus described in 1821. When 

 in 1 841 Johannes Miiller wrote upon the structure of the Crinoidea, not a single 

 genus belonging to this group had been proposed, and not until 1877 was the 

 type upon which it was founded recognized as of more than family importance. 

 This slow progress of investigation in a group which is now represented by 31 

 genera was primarily due to the rarity of their occurrence. Of the first genus, 

 Taxocrinus, founded by Phillips in 1843, probably not half a dozen specimens 

 were known in England. De Koninck and Le Hon's type and only European 

 species of Forbesiocrinus, from the Belgian Carboniferous, was only known by 

 their two original specimens from 1854 until I obtained the new material 

 figured in this work. Three species belonging to this group were quite abun- 

 dant at the celebrated locality of Crawfordsville, Indiana, and have been dis- 

 tributed among the museums of the world in later years; but aside from these 

 the Flexibilia have been, and are to this day, among the rarest fossils in the 

 rocks. Some localities with an abundant crinoidal fauna have not produced 

 a single specimen belonging to this group. 



This paucity of remains is not due to any special fragility of construction ; 

 on the contrary these fossils are for the most part well adapted to preservation. 

 As the name indicates, the group is characterized by a certain flexibility of the 

 calyx due to the presence of loose sutures with elastic ligament between the 

 plates, admitting of considerable mobility. At the same time the plates are 

 usually very thick, their depth frequently exceeding their length or width, so 

 that the apposed faces are relatively large, and the plates are fitted' together 

 like bricks in a pavement. Consequently in the process of fossilization the 

 calyx was not easily broken by pressure, but tended to remain intact when 

 enveloped by the mud of the sea bottom, although yielding to some extent, and 

 therefore in many cases found flattened in the rocks. In some genera, how- 



1 Philosophical Transactions, Roy. Soc. London, vol. 52, Pt. I, p. 357, pi. 13, Fig. B. 

 ' Organic Remains of a Former World, vol. 2, pp. 258, 270, 274, pi. 19, fig. 2. 

 3 The History of Rutherglen and East-Kilbride, pi. 18, figs. 13, 16. 



