PLATE IV. 



POTERIOCRINUS DORIS (Hall). 



Upper Burlington Limestone. Burlington, Iowa. 



Fig. 1. A mature individual, with arms and ventral sac nearly complete, and part of 

 stem, posterior view ; the sac tapering rapidly beyond the arms, and terminating 

 in a narrow point, shown by imprint in matrix. Pinnules do not show plainly, 

 being obscured by matrix. 



2. Another specimen seen from same side, with ventral sac more .sharply preserved; 

 both show the fine siiborfiinate striations passing from plate to plate in the inter- 

 vals between the larger plications of the calyx. 



•i. Anterior view of smaller specimen to first brachials only, with sharper and finer 

 folds; sjiowing transverse ridge upon radial facets. 



4, 5, 0. Three much younger specimens with arms and ventral sac, having relatively 



longer brachials than the mature specimens, and showing well the small pinnules. 

 These are either the young of the same species as the preceding, or with Fig. 3 

 belong to a different species morphologically in the yoimger stage, as indicated 

 by the relati\ely long anfl slender brachials. Figs. 4 and 5 are much flattened, 

 otherwise they would appear slender as Fig. (i, which is of about normal width. 



PoTERIOCRINUS M.\CROPLEURUS (Hall). 



Lower Burlington Limestone, Burlington, Iowa; Lake Valley, New Mexico. 



Fig. 7. One of the types, in the Barris Collection, Mus. Comp. Zoiil., Har\'ard; part of 

 large calyx with base wanting. One radial facet is occupied by two very short 

 brachials in succession irregularly; the upper joint face seems to be a syzygy. 



5. The other type, calyx of smaller specimen, formerly in collection of Dr. Otto Tliieme; 



showing facets with transverse ridge. 

 9. Calyx of large specimen from Lake Valley, New Mexico, anterior view; not com- 

 pressed, and giving the normal contour; a very short IBr in place. 

 10, U. Detached radials as usually found at Burlington. 



Cyathocrinus sp. 



Knobstonc Group, Button mould Knob, Ky. 



Fig. 12. Radial of smooth form, showing undifferentiated, concave, horseshoe shaped 

 articulating facet, without transverse ridge, fossae, or other sculpturing. 

 13. Radial of highly ornamented species, with relatively smaller facet, showing same 

 structures. 



Barycrinus tumidus (Hall). 

 Keokuk Limestone, Keokuk, Iowa. 

 Fig. 14. Calyx with IBr slightly displaced, showing the concavo-convex apposed faces. 



