Remarks on the Genus Pterotocrinus. 



REMARKS OX THE GEJ^fUS PTEROTOCRINUS, 



Lyon and Casseday. 



By a. G. Wetherby, A.M., 



Professor of Geology and Zoology, University of Cincinnati. 



Asterocrimis Lyon ; Geological Survey of Kentuc/cj/, old series, 

 vol. iii., p. 472, pi. iii., figs, la to 17c. 



Dichocrinus Shumard ; Transactions St. Louis Academij of Science, 

 Fe*bruaiy 9, 1857. 



Pterotocrinus, L3'ou and Casseday ; American Journal of Science 

 and Arts, Vol. xxix., p. 68, January, 1859. 



In the third volume of the Geological Survey of Kentucky, old 

 series, page 472 et seq., Mr. L^'on described, under the names Astero- 

 crinus capitaHs and Asterocrinus coronarius, the first species of the 

 remarkable genus which we now have the means of somewhat more 

 fully understanding, and of referring to a more definite place among 

 the Paleocrinidoi. 



In the article published in the American Journal of Science and 

 Arts, to which reference is made in the S3nionymy above given, the 

 name of the genus was changed to Pterotocrinus, that previously as- 

 signed to it proving to be pre-occupied ; and the autliors, Lyon and 

 Cassedaj', published three new species. In the descriptions of these 

 some facts were added to the previous knowledge of this genus, and 

 its generic formula was arranged as follows : Basal pieces, 2 ; radial 

 pieces, 1st series, 5 ; radial pieces, 2d series, 10 ; radial pieces, 3d 

 series, 20 ; anal pieces, 1 or more; mouth central, 1; column round (?); 

 arms ciliated and single, 20 ; wings or lobed pieces, 5, variously formed. 



Up to this time, or for a period of nearly twenty years, nothing- 

 further has been added to our knowledge of this anomalous genus, but 

 few additional species having been referred to it, and part of these er- 

 roneousl}'. It is now proposed briefly to review the whole subject, and 

 to add such facts as have been derived from the stud}"^ of a large series 

 of specimens, some of which are far more perfectl}^ preserved than any 

 hitherto discovered, while others are broken or distorted in such a 

 way as to show many parts of the structure in the most satisfactory 

 manner ; so that we now have the means of adding such new facts as 

 will render our understanding of this fossil comparativel}' complete. 



The Body. 

 The body of this Crinoid consists of a saucer-shaped shallow cup in 

 some species, ur of a much deeper, sub-conical one in others. This 

 arises from the different form of the pelvic plates in the various species 



