INVERTEBRATES. 315 



This species seems to be closely related, so far as 

 our specimens show its structure, to some of the 

 forms referred by Prof, de Koninck to his genus 

 Hydreionocrinus (Mem. de JPalseont., Bull., Acad. 

 Roy. Belyique (2) tome iii, p. 22). Indeed, if 

 his H. scoticus, of that paper, really belongs to 

 that genus, we can scarcely doubt the propriety of 

 calling our species Hydr. crassus; but as neither 

 our crinoid nor the species scoticus are known to 

 possess the remarkable structure of the upper parts 

 seen in Hydr. Woodian'us, the type of that genus, 

 we are left in doubt on this point. 



Zeacrinus? crassus.— (Nat. size.) T 7 . . . . . -,-, ,, , 



Diagram showing the small basal Locality and position: Avon, Fulton county, 

 &ndV n a a^ie^e 3 radial8 ' flrrt r * HI. J lower part of Lower Coal Measures. 



Genus ERISOCRINUS, M. and W. 



Synon. — A Crinoid near Encrinus moniliformis, Marcou, 1864. Bull. Geol. Soc. France, 

 tome xxi. 



Erisocrinus, Meek and Worthen, March, 1865. Am. Journal Sci., 2d series, 

 vol. xxxix, p. 174. 



Philocrinus, Meek and Worthen, May, 1865. Ibid. ; (not de Koninck, 1863.) 



Erisocrinus, Meek and Worthen, Aug., 1865. Ibid. ; p. 148. 

 Generic formula. — 



Basal pieces, 5. "\ 



Subradials, 5. v- United to form the walls of the body. 



Radials, 5+2. J 



Anal and interradials, 0. 



Arms and vault unknown. 



Basal pieces very small, forming a pentagonal flattened or 

 concave disc, or a low cup. Subradials larger, not varying in 

 form, and all alternating with the basal pieces. First primary 

 radial pieces considerably larger than the subradials, with 

 which they all alternate ; all connecting laterally, so as to leave 

 no spaces for anal or interradial pieces, and truncated their 

 entire breadth above for the reception of the next range of 

 pieces. Second radials of near the same size as the first, and 

 like them, connecting all around — supporting on their superior 

 sloping sides the first divisions of each ray. 



