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636 THE CRINOIDEA CAMERATA OF NORTH AMERICA. 
nally 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 Wachsmuth and Springer. 
Remarks. — This species differs from all preceding 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 Meek and Worthen as Actinocrinus penicillus, 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 Telewcrinus, 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 Telewcrinus adolescens, which 
to the top of the arms must have been four times as large as those spcci- 
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 1s composed of comparatively few and large plates, most of them 
spiniferous, but there are no small plates interposed between them. 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, _ 
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