Carboniferous Rocks of the Mississippi Valley. 325 



ly tubcrculose plates, with broad, rounded, elevated sur- 

 faces. In external characters it bears some resemblance 

 to the Gilbertsocrinns Americamts, (Tioosi,) from the Silu- 

 rian strata of Tennessee. In one specimen, one of the 

 postero-lateral rays has two radial plates instead of three, 

 which consequently has shortened the anal area. 



Geological formation and locality. At the junction of 

 the Chemung rock with the Burlington limestone, Burling- 

 ton, Iowa. Collection of C. A. White. 



Rhodocrinus Whitei var. Burlingtonensis. Body of the 

 form of R. Whitei. Basal plates small, lying at the bot- 

 tom of the cavity, and forming by their union a somewhat 

 regular pentagon, concave towards the middle, and entirely 

 covered by the summit of the column when present. The 

 sub-radial and radial plates are the same as in the typical 

 forms. 



The principal differences are in the greater number of 

 interradial and anal plates ; this, with a diameter half as 

 great as those, has from twelve to fifteen arranged in series 

 of one, three, three and three or four, with two or three 

 others, and sometimes another series of two. The body 

 plates are not so tubcrculose, being regularly but highly 

 convex. 



If these characters are found to be constant, they may 

 be sufficient to constitute a distinct species. 



Geological formation and locality. With the preceding. 

 Collection of C. A. White. 



Trematocrinus reticulatus (n. s.). Body sub-ovoid or 

 sub-cylindrical, slightly spreading at the arm bases ; base 

 deeply and abruptly concave. Basal plates very small, 

 forming the bottom and about half the sides of the basal 

 concavity. Sub-radials heptagonal, their centres forming 

 the lower margin of the cup, the lower half curved into the 

 cavity, and the outer half ascending. First radials hep- 

 tagonal, about the same size as the sub-radials; second 



