6 UINTACRINUS: ITS STRUCTURE A.ND RELATIONS. 



it is by such broken specimens that some of the most important informa- 

 tion touching the structure of these Crinoids has been revealed, whicli 

 would perhaps not have been discovered had all the specimens come out 

 uninjured. 



The Crinoids are found in all positions. The majority of them lie on 

 their sides. Many were embedded base downward, leaving that exposed and 

 uppermost upon the slab now. Several were found, fortunately, with the 

 ventral side of the calyx down and buried in the matrix, and these proved 

 to be gems of the first water. The arms are sometimes closely folded, but 

 more often opened out. We do not always see the calyx belonging to a 

 good set of arms, because the calyx was enclosed in the mass of Crinoids, and 

 only the arms happened to be on the lower side of the floating mass so as to 

 be buried and preserved in the soft sea-bottom. So the arms will now seem 

 to run into the hard limestone layer toward some calyx which was crushed 

 out of all shape and cannot be exposed now by removal of surrounding 

 material. So, vice versa, a fine, plump calyx which was on the lower outside 

 of tlie floating colony is shorn of some of its interest as a specimen, because 

 the arms run into the limestone slab, and are lost. Considering that they 

 were all entangled by the arms and pinnules, it is to be expected that speci- 

 mens fully exposed would be rare. Nevertheless, many splendid specimens 

 were secured, by which we are able to work out the morphology of this 

 interesting Crinoid to a degree of satisfaction rarely, if ever, before obtained 

 in a fossil. One of the finest of the slabs from this colony may now be seen 

 upon the wall near the entrance of the Museum of Comparative Zoology at 

 Harvard College. It is about eight feet by four, and contains about one 

 hundred and twenty-five Crinoids, many of them with long arms, and finely 

 preserved. 



The walls of the calyx of these Crinoids are thin, and the plates are' 

 apparently connected by a sort of articulation, or loose suture. The calyx 

 was very large and light, and without rigidity. All are crushed so that the 

 opposite walls are brought together in the form of a concavo-convex bowl. 

 The superincumbent weight pressed the undermost wall into the soft mud, 

 and the uppermost wall into the concavity thus formed. Specimens that 

 now appear convex and plump upon the inverted surface of the slab have 

 the opposite wall pushed into a concavity equal to the convexity of the 

 outer exposed wall. Occasionally the calyx comes entirely loose from the 

 matrix, and we find the opposite wall in the concave part underneath. 



