Ii)4 SMITHSONIAN INSTITUTION 



Mespilocrinus konincki Hall 

 Plate V , figs. 4-15 



Mespilocrinus konincki Hall, Supplement Geology of Iowa, I, i860, p. 69; Bull. N. Y. St. Mus. Nat. 



Hist., I, 1872, Photo. Plates, pi. 6, fig. 9. — Wachsmuth and Springer, Revision Palaeocrinoidea, 



pt. I, 1879, p. 42. 

 Mespilocrinus scitulus Hall, Jour. Bost. Soc. Nat. Hist., VII, 1861, p. 321 (Prelim. Notice, p. 9; Bull. 



N. Y. St. Mus. Nat. Hist., I, Photo. Plates, pi. 6, figs. 7, 8. 

 Cyathocrinus blairi Miller and Gurley, Bull. 7, Illinois St. Mus., 1895, p. 67, pi. 4, figs. 13, 14, 15, not 



figs. 11 and 12, nor ibid., Bull. 8, p. 50, pi. 3, figs. 21, 22, nor ibid., Bull. 9, p. 39. 



A small species. Crown globose, height and width equal, widest about 

 I Ax; height to width there about I to 1.6. Base broad; spread of calyx from 

 base to RR, about 1 to 2.5; cross-section circular. Surface smooth. Maximum 

 crown, 8 mm. high by 8 mm. wide ; average, 6 by 6 mm. 



IBB of medium size. Post. B rising nearly to height of RR; other BB and 

 RR about equal in height, and IBr about two-thirds as high; B to R to IBr, 

 2.5:2.4:1.5. RR evenly curved; succeeding plates broadly rounded. IIBr 

 mostly 2. Anal x large, filling interradius. Rays in contact, infolding, closing 

 below the third bifurcation ; arms with marked dextrorse twist. Column large, 

 composed near the calyx of short, uniform, rounded columnals, which gradually 

 increase in length ; from the fifteenth to twenty-fifth they become greatly elon- 

 gated, widening in the middle and narrowing at the sutures until they become 

 doubly conical, or spindle-shaped; the average proportions of a fully developed 

 columnal of this kind are : length to width in middle, 2 to 1 ; to width at ends, 

 4 to 1. 



This species was the first example of the genus recognized in America, Hall describing 

 it from a very small specimen. It is from the Lower Burlington limestone, a horizon which 

 in general faunal characteristics has much in common with the Mountain limestone of 

 Belgium. It has always been a rare fossil at Burlington, but by good fortune I have been 

 able to secure about a dozen excellent specimens, so that its peculiar characters can be 

 thoroughly illustrated. The dextrorse twist of the arms is a very singular feature ; looking 

 at the specimen with the calyx erect, as we ordinarily do, the arms bend more or less to the 

 right, some tending to pass under the adjoining ones. There is in connection with this a 

 certain amount of irregularity in the form and size of the radial and brachial plates not usual 

 in crinoids. The whole aspect of the crown is that of a rather irregularly rounded, somewhat 

 asymmetric, globose cluster of short, thick arms. Along with this peculiarity there is the 

 extraordinary stem, which in the extreme length of the median columnals is quite unique ; and 

 it usually tends to coil around the crown something after the fashion of Herpetocrinus and 

 Camptocrinus. We can in practice always recognize the species from a small fragment of 

 the stem or crown. 



Compared with De Koninck and Le Hon's figures, it is not easy to distinguish this species 

 from M. forbesianus by the crown alone. The general proportions and the relative dimen- 

 sions of various plates are not very different, and the characteristic twist is equally promi- 

 nent in both. Hall distinguished them easily in his description by the phrase which has since 

 done duty at the birth of so many doubtful species : " This small species bears considerable 

 resemblance to M. forbesianus of De Koninck and Le Hon, but differs much in the form and 



