148 PAL5:0NT0L0GY OP NEW-YORK. 



NOTE. I am indebted to Lbdtakd Liiicki.aics, esquire, for the luagnillccnt specimen of tlie luost bcau- 

 tiftil species of this genus, Mariacrinm nobiliisimut, figured on Plate II. Tlie large specimen figured on 

 Plate II A was obligingly lent to mo by Col. E. Jkwett. 



Plattchlkus plumostts. I should have noticed in its proper place the close resemblance between this 

 species and Marsupiocrinua calatxts, MuRcnisoN, Sil. System, pa. G72, 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. We are not 

 informed, however, whether these later discoveries demonstrate the original supposition of Professor 

 Philups, that the sj»cies has five pelvic plates. The original description is " pelvic plates unknown 

 ( probably five)." From the remarkable analogy in all the superior parts of Marsupiocrinites ceelahis 

 with Plaiycrimu pliimosiu, I cannot avoid the presumption that the British species is a true Platy- 

 crintu, 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 arc 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 Platycnn%is in Great Britain, as in the United 

 States, during the Upper Silurian period. 



DiCTTOCKiNUS. Under this genus I omitted to remark upon its supposed relations with Ischadites of ^ 

 MuRCHisoN, Sil. System, pa. 097, pi. 20, f. 11. Indeed the figures in the Silurian System bear so close 

 a resemblance to ReeeptaculUes, that I could scarcely regard them as distinct fi-om that genus. Mr. 

 Morris, in his Catalogue of British Fossils, cites Ischadites kanigi as .synonymous with Receplaculites 

 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 Orbittdites? rtlicidata ; and in his Geological Report of Iowa, Wiscon- 

 sin and Minnesota, 1850, pi. 2 b, f. 13, as Sdenoides iowensis, 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 me 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 fo.ssil, having as he thinks 

 some relation to Ischadites of McKcnisoN, may perhaps include forms like Dictyocrinus ; but if the 

 fossil described and figured by Profsssor M'Cor in his Descriptions of the British Palaeozoic Fossils 

 in the Museum at Cambridge, pa. 02, pi. 1 n, f. 7 & 8, be a true Telragonis, I would hesitate to include 

 under that designation either Ischadites or Dictyocrinus. 



With the materials at present possessed, I can express no satis&ctory opinion as to the relations of 

 Dictijocrinus ; 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. Owkn as above cited, which I regard 

 as belonging to the Genus Receptaculites. 



