636 THE CEINOIDEA CAMEEATA OF NORTH AMERICA. 



nallj arranged. Ventral disk barely rising above the rim, and deeply 

 grooved interradially and interdistichally, the middle part conical, passing 

 imperceptibly into the anal tube. The tegmen is composed of a large 

 number of very small, slightly convex pieces, which enclose a few larger, 

 sharply nodose or subspinous plates, among which the orals and radial 

 dome plates of a first and second order are readily recognized. Tube 

 central, large and long, constructed of irregularly arranged, transversely 

 nodose plates. Column slightly hexangular; the axial canal large and 

 pentangular. 



Horizon and Locality. — Lower Burlington limestone, Burlington, Iowa. 



Types in the collection of Wachsnmth and Springer. 



Remarks. — This species differs from all pi-eceding ones in having a less 

 number of arms, and deeper interradial sinuses at the rim, which are caused 

 by a slight gap between the arms of adjoining rays. 



The small specimen in the Museum of Comparative Zoology, described 

 and figured by Meelc and Worthen as Adinocrinus peivixMus, represents most 

 probably a very young stage of this species. If, however, it is an adult 

 form, which we think doubtful, it is certainly not a Teldocrinus, for the 

 branches of the rays from above the distichals take the form of free arms, 

 although directed almost horizontally and crowded together as in that genus. 

 We found also in our own collection two small specimens, evidently of the 

 same species as the Cambridge one, and morphologically in the same con- 

 dition. In one of them we removed the arms on one side, and exposed 

 the tegmen and anal tube, so as to enable us to see the form of the calyx. 

 The length of the specimens to the tips of the arms does not exceed the 

 height of the conical part of the dorsal cup in Teleiocrinus adolescens, which 

 to the top of the arms must have been four times as large as those speci- 

 mens. The latter have but five interbrachials at the regular sides, and 

 about eight above the anal plate, against eight and thirteen in the larger 

 form. The arms to the fourth or fifth plate are uniserial, the joints long, 

 cuneate and zigzag, as usual in very young specimens. The tegmen is- 

 conical, resembling the "part which in the larger specimens lies inside the 

 rim ; it is composed of comparatively few and large plates, most of them 

 spiniferous, but there are no small plates interposed between tliem. Both 

 forms have ten arms to the ray — exceptionally- eight or nine — which bifur- 

 cate in the same manner. The proportions of the plates, and the surface 

 ornamentation as well, are also quite similar. So far as can be ascertained, 



