59 



specimen represented by figure 17 has the ray on the right of the 

 azygous area bearing four arms, and the arm formula is 4+3+2 

 +3+3. It will be noticed that throughout all these variations 

 the ray opposite the azygous area has two arms, and the four- 

 armed ray changes its position to each of the other rays. 



There is only a single plate in each of the four regular inter- 

 radial areas in the specimens represented by figures 13., 14 and 

 16. And there are two plates in each of the regular interradial 

 areas, in the specimens represented by figures 15 and 17. In the 

 azygous area, in the specimen represented by figure 13, there are 

 six plates. The first one is in line with the first primary radials 

 and as large as either one of them. It is followed by three plates 

 in the second range, subequal in size, and above these, there are two 

 plates, one of which unites with the two plates belonging to the 

 vault. The specimen represented by figure 17 has the same num- 

 ber of plates in the azygous area, but there is a little difference 

 in the arrangement of the plates at the upper part of the area. 



The specimen represented by figure 16 has seventeen plates in 

 the azygous area. There are two small plates instead of one in 

 the third range. 



The vault is more convex in some specimens than in others, 

 the proboscis is larger in some specimens than in others. The 

 number and arrangement of the plates covering the vault is quite 

 different in different specimens, as shown in figure 14 and 17. 



Notwithstanding all these variations, we place all these forms 

 in the same species, because, in each one, the number of ambu- 

 lacral openings to the vault is the same. Other differences might 

 be pointed out from other specimens, as, for example, some speci- 

 mens have a single plate, in some of the regular interradial areas, 

 and two in others, but those pointed out are the controlling varia- 

 tions. 



There has never been but one fifteen- armed species heretofore 

 described, from the Burlington Group, and it has no resemblance 

 to this one. The affinities of this species are with B. verneuili- 

 (inus and the two species are to be distinguished by the number 

 of ambulacral openings to the vault. We have examined several 

 hundred specimens of B. verneuilianus, and, while they differ in 

 size, form and regular and azygous areas as much as the species 

 here under consideration, they always have fourteen ambulacral 

 openings to the vault. When Shunard described B. verneuili(mus> 

 he called it an Aclinocrinus, because the genus Batocrinus was 

 then unknown, and following the ordinary structure of Actino- 

 crinus, in his definition, he said there were only two plates, in 



