STRUCTURE OF THE CYSTIDE^. 



29 



conduct the ambulacral canals towards the summit of the ventral 

 side. 



6. Pradocrhms Baylii (deVerneuil*), a species which occurs in the 

 Devonian rocks of Sabero, in Spain, has ten ambulacral apertures 

 very clearly exhibited. The ventral surface of this fine species 

 consists of numerous small plates, the mouth is excentric, and there 

 are ten arm.s. The apertures are formed by a notch in the second 

 plate of the secondary radials on one side, and on the other by 

 several small ventral plates, as in Actinocrinus stellaris. Grood 

 specimens are in the collection of the Geological Survey of the 

 United Kingdom, Jermyn Street. See also the figures given in the 

 work cited. 



Among the species figured in various works, the following are 

 some that shew these apertures very distinctly : — 





Mrw^\ 



Fig. 13. Fig. 14. 



Figure" 13. Dolatocrinus lacus (Lyon). Side vie-w^. 



" 14. Diagram of one of the rays. 



" 15. View of the ventral surface. 



Fig. 15. 



Dolatocrinus lacus occurs abundantly in the Devonian formation 

 of Kentucky, and the above figures are taken from the beautifully 

 illustrated Report of Mr. Sidney S. Lyon, of the Geological Survey 

 of that State, published in 1857. (Plate iv. figs. 2, 2a, 2b.) There 

 are ten ambulacral orifices, and the mouth is central, but there are 

 no grooves from it to the arms. The generic figure given by 

 Mr. Lyon— of which the above fig. 14 is a portion— shews all the 

 apertures. In the same plate there are several figures of another 

 species, Vasocrinus valens (Lyon), with five orifices; but of these 

 only the grooves on the inner margins of the primary radials are 

 preserved. All the ventral plates appear to be absent, and it 



Bulletin Geo. Soc. France, 2d series, 1850, vol. vii. page 184, plate iv. fig. 11. 



