iu 



is on the right of the azygous area, there is only one plate in each 

 regular interradial area, and five plates in the azygous area, 

 1+3+1. The question presented is whether or not these differ- 

 ences are of specific importance. A single additional small plate, 

 in any one interradial area could hardly be claimed to be of 

 specific importance; and, for the same reason, we think the ad- 

 ditional small plate, in each area, is not of specific importance. 

 We allow for greater variation, in the interradial area, within the 

 limits of a species, than we do in the arm formula, in the calvx, 

 and yet, there is an absence of definiteness, in a description, that 

 reads "one or two regular interradials and five or six azygous 

 plates." However, in this case, it is a small plate that is absent, 

 in each area, and which does not noticeably change the form of 

 the body. 



Having disposed of these differences, the question still remains, 

 whether or not the arrangement of the five-armed ray on the 

 right or left side of the azygous area is of specific importance. 

 We think it is not, and this leads us to some general remarks con- 

 cerning the structure of crinoids. We think the azygous side of 

 the calyx is the anterior side and the opposite side the posterior 

 side. The early palaeontologists took the contrary view, and much 

 of the literature is written that way, ard Billings, doubting the 

 correctness of the old view, and probably believing as we do, pro- 

 posed the use of the word azygous, as applied to one side, and 

 we have followed his method of nomenclature, in order that our 

 definitions might the more readily be compared with the work of 

 others. Believing that the azygous side is the anterior side of the 

 crinoid, we can see no reason why, iu a twenty-one-armed species, 

 it should be deemed material whether the five armed ray is on 

 the right or left side of the front interradial space, and the ex- 

 amination of large quantities of material belonging to many species 

 seems to u^ to indicate that it is not of specific importance. But 

 it does seem material, whether a five-armed ray is on the anterior 

 side, in one specimen, and on the posterior side in another; for 

 here the variation is in essentially different parts of the body, and 

 our observations, in all cases, even in Batocrinus variabilis, con- 

 firms this view. 



We are aware that some pseudo-biologists call the vault the 

 ventral side of a crinoid and the calyx the dorsal side; but the 



