INVERTEBRATES. 85 



Basal plates very small and concealed in the basal cup. First 

 m dials once and a half as wide as the second, and projecting; so 

 as to form a prominent rim around the basal cavity. 



Second radials quadrangular, nearly twice as wide as long. 

 Third radials pentagonal, axillary, and supporting on their upper 

 sloping sides the secondary series. 



The secondary and tertiary radial series, consist of three 

 plates each, the last one of the third series giving support to 

 the first arm plates. 



First anal plate hexagonal, and succeeded by two smaller ones 

 in a double series. 



Arms composed of a double series of closely interlocking 

 plates. 



Ventral tube slender; column unknown. 



Position and locality: St. Louis division of the Lower Car- 

 boniferous. Union county, Illinois. 



No. 2581 of the Illinois State Museum. 



BATOTRINUS NASHVILL.E, Troost, sp. 



PL XIII, Fig. 5. 



This magnificent crinoid wa.s described and figured in the 

 (Jeology of Iowa, Vol. I, part 2, page G09, pi. XV, fig. 4, and 

 pi. XVI, figs. 4, a & b, under the name Actinocrinus nashvillte 

 Troost; but none of the specimens known at that time had the 

 remarkable ventral tube belonging to this species preserved, 

 and an individual in which that organ is well preserved, is here 

 illustrated. 



The following is the original description of the species: "Body 

 urn-shaped, rounded at base and excavated for the reception of 

 the column, contracted above, and somewhat rapidly expanding 

 at the brachial margin; dome moderately elevated, with a strong 

 central proboscis. Basal plates more than twice as wide as 

 long, spreading in a broad thickened rim, indented at the line 

 of suture. First radial plates large, wider than long, tubereu- 

 lose transversely, and prominent above the other plates. Second 

 radials wider than long. Third radials supporting on the two 

 upper oblique sides, two hexagonal supra-radial plates, and these 

 support two brachial plates, from the upper sides of which pro- 

 ceed the arms, giving uniformly four arms to each ray. A small 



