Maryland Geological Survey 249 



qass CRINOIDEA 



Order CAMERATA 

 Family THYSANOCRINIDAE 



Genus THYSANOCRINUS Hall 



Thysanocrinus eugenius n. sp. 

 Plate XXXVI, Figs. 3-7 



Description. — Body medium in size, urn-shaped, truncate dorsally, the 

 infrabasals and the lower parts of the basals forming the base of the body ; 

 wall of body almost straight below arm bases. Infrabasals 5, protruding 

 beyond the periphery of column ; basals 5, largest of the calyx, extremely 

 convex; posterior basal larger than the rest and truncate above; the 4 

 lateral basals hexagonal, angular above ; radials larger than costals, very 

 convex and prominent heptagonal, angular below, truncate above ; costals 

 2x5, very convex, prominent, the first hexagonal, truncate above and 

 below, the second pentagonal, truncate below, angular above, each side of 

 angle bearing a distichal ; distichals 4 ( ?) x 10, the first larger than the 

 rest which are transversely elongate, the last one often bearing a short, 

 stout spine ; arras 10, simple, biserial, composed of alternating cuneiform 

 plates, and often bearing at fairly regular intervals a single spine or even 

 a pair; pinnules not seen; intercostals 3 — one in the first series, large 

 hexagonal — two in the second series, hexagonal, smaller than the first and 

 situated above it and between the second costals ; interdistichals 5 or more, 

 small ; interradial areas much depressed below the radial ; anal interradial 

 wider than the others, the first plate large, conspicuous, highly convex, 

 resting on upper truncated edge of posterior basal and between the postero- 

 lateral radials, three plates in the second series, the middle one most 

 prominent and resting directly upon the first series, other series present 

 (indeterminate in specimens examined), the middle one always the more 

 prominent by its convexity. Stem and tegumen unknown. 



Four individuals of this species are known to the writer. Of these two 

 have spinose arms while the others seem to be without this feature. Never- 

 theless, unless further collections show this to be other than a specific 

 variation, all must be regarded as one species. 



