29O SMITHSONIAN INSTITUTION 



found higher up, and it shows that there was no extraordinary growth of calcareous matter 

 at this point to render the external contour specially different from the internal. The basals 

 themselves are very small, though they would be somewhat larger at the exterior ; and in view 

 of the apparent condition of the infrabasals, and what we know of their relative proportions 

 in other species, it is clear that the basals were nearly, if not quite, covered by the column, and 

 not visible externally in a side view. 



The straight sutures on which Winchell and Marcy laid so great stress are not a valid 

 specific character. As before explained in the chapter on Morphology, the sinuous suture 

 lines and so-called " patelloid plates " throughout this entire group are only external surface 

 characters which disappear by wear, all sutures becoming straight a short distance inward. 

 The fact as to this particular species is beautifully shown by the specimens preserving part 

 of the test figured on Plate XXXVI, figures 6a, b, where both kinds of sutures are shown in 

 the same parts of the same specimen. 



This species is distinguished from /. laevis, which is nearest like it in the size and imbri- 

 cation of the plates, by the pyriform crown and larger basals of that species. It is nearest 

 in general form and probably in details of the base to /. gotlandicus, the type specimen of 

 which was originally identified by Angelin as I. laevis, but it differs in the absence of 

 ornamentation. 



Types. The original specimens used by Winchell and Marcy are understood to be in the 

 Northwestern University at Chicago, but as none were figured they cannot be identified. 

 Those figured herein are in the author's collection. 



Horizon and locality. Silurian, Racine dolomite beds of the Niagaran Group ; Chicago, 

 Illinois, at quarries about the junction of Thirty-fifth street and Archer avenue, formerly 

 known as Bridgeport. 



Ichthyocrinus devonicus n. sp. 



Plate XXXV, figs, iya-c 



A small species of the type of Ichthyocrinus gotlandicus, but with calyx 

 more broadly spreading" and somewhat pyriform in lower part. Height to width 

 at upper IIBr, 1 to 2; spread of calyx to that level, 1 to 5. Crown ovoid to low 

 pyriform; no radial ridges. Surface smooth; plates not imbricated. Crown, 

 about 30 mm. high by 25 mm. wide ; base, 5 mm. 



IBB, BB, and RA covered by the column. IIBr 3; IIIBr 3 to 7; height to 

 width of Br above IBr, about 1 to 3.5. Column large at base, unknown below 

 proximal columnal. 



This species is founded upon a single specimen from the Helderbergian of Tennessee — 

 the only Devonian representative of the genus from American rocks. It is of the type of 

 /. corbis and /. gotlandicus in the extreme reduction of the basal elements, and it agrees with 

 the latter and differs from all other American species of this genus in having but three IIBr; 

 these characters produce a short and broadly spreading calyx. 



Type. Author's collection. 



Horizon and locality. Devonian, Linden formation of the Helderbergian ; Benton 

 County, Tennessee. 



