thr Criuoidea, Cysticloa and Blastoidea. 



253 



imbedded in and tunn a jjortioii of the general covering of the 

 body, or lie upon the .surface, or be borne upon free-moving 

 arm-s. In genera belonging to the same familythe.se relations 

 are constant or nearly so, but are found to be extremely vari- 

 able when ditferent orders or remotely allied families are 

 eomparetl. 



\Vhile jireparing my Decade Xo. 3, I investigated this sub- 

 ject, and satisfied myself that in at least a large proportion of 

 the })ala'OZ()ic Crinoids the mouth was disconnected altogether 

 from the ratlial system. A great many species might be re- 

 ferred to in which we can see both the centre from which the 

 ambulacra proceed, and the mouth, and at the same time see 

 that they are not in the same place. A long train of reason- 

 ing is not necessary, only simple inspection. It will be quite 

 sutiicient to notice a few of these species to prove that the 

 rule laid down by Prof. \Vy\illc Thomson is not a general 

 rule. 



Fiff. 1. 



Fisr. 2. 



Fi!?. 3. 



Fig. 1. This figure is a diagram of the interior of the vault 

 of a Crinoid Avhich appears to be Batocrinus icosirJacfylus 

 (Cassiday), a fossil that oeciu's in the Carboniferous rocks of 

 Kentucky. It was sent to me by Mr. S. S. Lyon, of Jefferson- 

 ville, Indiana, several years ago. The test is in a beautiful 

 state of preservation, and perfectly empty, so that all of the 

 markings on the inner sm-facc can be distinctly seen. There 

 are twenty-one anus arranged in five groups («), and the same 

 number of ambulacral openings (/;), each just large enough to 

 admit of the entrance of a slender pin. The mouth [mv) is 

 nearly central ; and close to it, on the posterior side, there is a 

 small rudely pentagonal space (c) with no markings except 

 several small tubercles. The grooves are scarcely at all im- 

 pressed ; and, indeed, I think they are never so in any Crinoid, 

 except in those which have a thick test. In this specimen 

 their course is clearly indicated by the remains of the thin 

 partitions which either separated them or to Avhieh the vessels 

 were attached. They do not run directly toward the mouth, as 



