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PALEONTOLOGY, 
ARCH. AMOCIDARIS. McCoy. 
ARCHAOCIDARIS LONGISPINUS, (n. sp.) 
Plate I, figs. 1 and la 
Interambulacral plates unknown. Spines elongate, fusiform, 25 to 33 inches in length, 
acute, with a cylindrical section at all points; surface smooth, or very finely and longitudinally 
striated. The ring at the base of the spine is small, slightly crenulated, and in my specimens 
encircles it at right angles to its axis; a character which, however, probably varies with the 
position of the spine. Below the ring the diameter of the base rapidly contracts, forming the 
frustum of a cone, of which the surface is concave. At the lower extremity of the spine a 
shoulder is cut in this cone, by which the diameter of the articulating surface is reduced to 4 
that of the ring. Spine straight throughout, with the exception of a very slight curve just 
above the ring, the greatest diameter exceeding that of the ring. 
The interambulacral plates of this species have generally not been preserved with the 
spines, as, in localities where the spines were abundant, I was unable to find traces of them. 
The spines are beautifully preserved, and present characters which separate this species from 
any heretofore known. Its smooth surfaces, entirely devoid of tubercles, and its circular sec- 
tion, distinguish it from those described by Prof. Swallow* and Prof. Hall.+ | As indicated 
above, there is great difference in the length of the spines; the shorter ones are much the more 
robust. The surface markings are, however, the same in all, and the variation in size and form 
is less than that exhibited in the spines of a single individual of any living species of -Cidaris. 
Locality and formation.—These fossils occur in great numbers in the crinoidal limestone in 
the upper part of the Carboniferous series on the banks of the Colorado river. They are so 
numerous in some localities that a dozen or more are visible on a square foot of the weathered 
surface of the rock. They seem to be strictly confined to this horizon, as I found none in the 
upper or lower of three Carboniferous limestones which are found in that region. 
ARCHHOCIDARIS ORNATUS, (n. sp.) 
" Plate I, figs. 2, 3, and 3a. 
_ Body unknown. Primary spines fusiform, robust, 2.50 inches long by 0.36 inch in diameter, 
hickly set with secondary spines .08 inch in length, arranged in imperfectly spiral lines; the 
points slightly inclined toward the remote end of the spine. Ring at the base of moderate 
size, crenulated. 
The spines of this species, in size and general form, resemble those of .A. longispinus, but 
are strikingly different in bearing a number of relatively large secondary spines which are 
: ‘separated from each other by intervals usually less than the diameter of their bases. : 
- From A. megastylis, Shumard, it is distinguished by the proximity and size of the secondary 
= spines, which are both much larger and more closely approximated than in that species. 
: tt - Proc. Acad. Nat. Se., St. Louis. + Geological Report of Towa, Vol. 2, p. 698, Xe. 
