102 
SMITHSONIAN INSTITUTION 
fourth arm, which is clearly specified in the description and figure of Castocrinus. But it now 
appears upon further examination in the light of subsequently acquired material that the 
fourth arm was actually present in the type specimen of Cremacrimis punctatus, now in the 
U. S. National Museum. Therefore the species of Cremacrimis and Castocrinus are generi- 
cally identical, and Cremacriniis, being the earlier in date, will be valid for the species falling 
under Form A. This conclusion is reinforced by the further fact, not mentioned in the 
description of either, that all species referred to the two genera in which it can be seen have 
the stem in the position at the right of the anal tube, which is such a fundamental character 
of Form A. 
That the fourth arm was not mentioned in the original description of Creniacrinus was 
owing to the imperfection of the type specimen upon which the genus and species were 
founded. This was apparently well preserved, and showed the median and two lateral arms, 
one on each side, as described. At the right of the anal tube, however, is a V3.cant space about 
the size of a lateral arm where the specimen had been attached tO' the rock, and from the 
information now afforded by several other specimens of the same species since obtained, it is 
evident that the missing arm was imbedded in the matrix and pulled off in collecting (pi. 28, 
figs. 16, i6a). With our present understanding of the structure, traces of the fourth arm 
may now be recognized in the type, but with no other guide than the imperfect original it was 
natural that the author should describe only what he could see, and frame his diagnosis 
accordingly. 
For the forms which had formerly been referred to Calceocrimis, and which would now 
fall under Form C, preference was given to Deltacrimis, which as before stated was proposed 
to take the place of Calceocrimis, rejected because lacking a type species. It was based upon 
Cheirocrinris darns Hall for genotype, a Middle Devonian species represented by the single 
type specimen from the Hamilton of New York. The species is so completely non-characteristic 
of the Silurian forms belonging to Form C, that I cannot reconcile the genus founded upon it 
with the highly distinctive characters for which they are so conspicuous. It entirely lacks the 
arched axil-arm system by which Forms C and D are distinguished from all other crinoids 
(text figs. iC, D, and pi. 29, figs. 7, 8, 9, 14, 20). This cannot be showin better than by the 
remarks of the author himself in his paper of 1886, from which I take the following extracts : 
On page no, under Halysiocrinus, it is said: 
“ In the formation of the dorsal side of the calyx this genus is precisely Deltacrimis. 
The only difference so far detected is found in the number of arms. In Cremacrinus we have 
three primary radials, and in Deltacrimis five ; while the species for which the above generic 
term is proposed have eleven, one large central arm on the dorsal side and ten smaller ones, 
the first pieces of which project abruptly outward and extend in a curved series transversely 
around the ventral side. Their inner ends articulate with the ventral arch.” 
By comparing my diagrams of Forms C and D in text-figure i, and various figures of 
Calceocrimis on plate 29, it will be seen that they have exactly the characters which are above 
ascribed to Halysiocrinus as distinguishing it from Deltacrimis. That the two forms cannot 
go together is further emphasized by the author in the continuation of his discussion on 
page 1 12: 
“ There are at least three American species that have the characters ascribed to Halysio- 
criniis. These are the C. dactyliis and C. nodosus Hall, and the C. wachsmuthi M. & W.. the 
first and last from the Burlington limestone and the second from the Keokuk Gr. Besides 
these the Chcirocrinns Gotlandiciis of Angelin is an unquestionable member of the genus 
.... In the construction of the body and in the possession of a strong dorsal arm, these 
species do not differ from Dcltacrinus. The lateral arms, however, differ conspicuously from 
all the species of both Cremacrinus and Deltacrimis in being much more numerous, subequal, 
and extending completely around the ventral side .... The ventral arms give to these cri- 
noids a different appearance from that presented by the more simple species of Cremacrinus 
and Deltacrimis. In my opinion they constitute an important dezmtion from the type of those 
genera, and fully zaarrant generic separation.’’ 
