STRUCTURE OF CALYX AND ARMS. 



The preservation of many of the Crinoids at Locality No. 1 is most ex- 

 cellent. The fine adherent matrix in which they were embedded can usually 

 be removed by careful preparation, leaving the surfaces of cup-plates, arms, 

 and pinnules exceedingly perfect; but it is useless to attempt to free the speci- 

 mens from the parts of other individuals with which they are entangled on 

 the slab. It is evident that the sea-bottom in which these fossils were 

 deposited was extremely quiet and undisturbed by currents, so that the 

 organic remains have been substantially unchanged as to their calcareous 

 skeletons, except by chemical action, resulting partly from the decomposi- 

 tion of the soft parts. In many respects this new material confirms the 

 account given by Mr. Bather. In the number and arrangement of the 

 interbrachial plates, which is said to be the chief point of difference be- 

 tween the American species and U. westf aliens, there is the greatest varia- 

 tion, — much greater than Bather supposed. He states that they vary from 

 7 or 8 to 12 ; whereas the range of variation is actually from 3 or 4 to 23, 

 as I shall show in detail later on. Clark's supposed definite plan of arrange- 

 ment of these plates does not hold good at all. He says : "^ ^^ The arrangement 

 of the plates does not vary ; seven in an oval band enclose the 8th, or 8th 

 and 9th, according to the number of interradials." While this is a frequent 

 arrangement, it is not at all a uniform one, as there are many cases where 

 the number of plates is greater or less than that stated, and many in which 

 they do not form a band enclosing one or more plates. The latter is true 

 for those which have 3, 4, 5, 6, or 7 plates ; these are disposed in two some- 

 what irregular vertical rows, with sometimes one of the plates forming a 

 sort of apex at the top between the two proximal pinnules (PI. V., Fig. 6) ; 

 it is also true for many areas containing 8, and sometimes 9 or 10 plates. 

 The variation in the interbrachial spaces is not confined to those of different 

 individuals, but is almost as great in those of the same individual. One 



* Bull. U. S. Geol. Suit., No. 97, p. 23. 



