148 
PALAEONTOLOGY OF NEW-YORK. 
NOTE. I am indebted to Ledyard Lincklaen, esquire, for the magnificent specimen of the most beau¬ 
tiful species of this genus, Mariacrinus nobilissimus , figured on Plate II. The large specimen figured on 
Plate II A was obligingly lent to me by Col. E. Jewett. 
Platycrinus plumosus. I should have noticed in its proper place the close resemblance between this 
species and Marsupiocrinus calatus, Murchison, Sil. System, pa. 672, pi. 18, f. 3; also Siluria, pi. 14, 
f. 1; and woodcut p. 219, f. 1, 2 & 3, the latter illustrating entire individuals and parts. Wc are not 
informed, however, whether these later discoveries demonstrate the original supposition of Professor 
Phillips, that the species has five pelvic plates. The original description is “ pelvic plates unknown 
( probably five).” From the remarkable analogy in all the superior parts of Marsupiocrinites calatus 
with Platycrinus plumosus, I cannot avoid the presumption that the British species is a true Platy- 
crinus, as is ours; having a very small base, with the sutures of the three plates faintly visible, but 
still leaving no doubt as to its true reference. 
The analogy is the more interesting, since the two forms are from rocks which are regarded as oc¬ 
cupying very nearly the same geological horizon in the two countries. Should it be found that the 
analogy in the entire structure is as close as the general resemblance and structure of the upper portions 
of the body and arms, it will prove the occurrence of Platycrinus in Great Britain, as in the United 
States, during the Upper Silurian period. 
Dictyocrinus. Under this genus I omitted to remark upon its supposed relations with Ischadites of 
Murchison, Sil. System, pa. 697, pi. 26, f. 11. Indeed the figures in the Silurian System bear so close 
a resemblance to Receptaculites, that I could scarcely regard them as distinct from that genus. Mr. 
Morris, in his Catalogue of British Fossils, cites Ischadites kanigi as synonymous with Receptaculites 
neptuni. The figures given by Dr. D. D. Owen in his Report of Explorations of Iowa, Wisconsin and 
Illinois in 1844, pi. 18, f. 7, as Orbitulites ? reticulata; and in his Geological Report of Iowa, Wiscon¬ 
sin and Minnesota, 1850, pi. 2 b, f. 13, as Selenoides ioivensis, bear a close resemblance to the figures, 
of Ischadites. The Illinois and Iowa specimens cited above*have all the characters of Receptaculites, and 
do not appear to mo to be related to Dictyocrinus. At the same time I have observed some specimens 
in the Schoharie grit of New-York, which, having the general aspect of Receptaculites in the form and 
arrangement of the cells or divisions of the surface, have been furnished with a pedicle precisely as in 
Dictyocrinus. The substance of the fossil has, however, been removed; and from those portions re¬ 
maining, it is not easy to determine positively their relations. 
The Genus Tetragonis, proposed by Eichwald in 1842 for a Silurian fossil, having as he thinks 
some relation to Ischadites of Murchison, may perhaps include forms like Dictyocrinus; but if the 
fossil described and figured by Profsssor M £ Coy in his Descriptions of the British Palaeozoic Fossils 
in the Museum at Cambridge, pa. 62, pi. In, f. 7 & 8, be a true Tetragonis, I would hesitate to include 
under that designation either Ischadites or Dictyocrinus. 
With the materials at present possessed, I can express no satisfactory opinion as to the relations of 
Dictyocrinus; but I can scarcely regard it ■as a cystidian, and I am quite satisfied that it has no 
relations with Receptaculites, or with the bodies figured by Dr. Owen as above cited, which I regard 
as belonging to the Genus Receptaculites. 
