Organic Remains. 221 



tween the ambulacra of the Crinoids and those of the Star-fishes, 

 in which it is well known that such organs do exist, renders it 

 quite certain that the former as well as the latter are provided 

 with a full set of ambulacral vessels." 



Figure 1. 



Figure 1. Diagram of the ventral surface of Pentacrinus caput- 

 MeduscE. The central orifice is supposed to be the mouth ; the 

 other, the anus. One of the grooves is represented as being 

 closed over by the marginal plates. 



"In many of the extinct species of Crinoids, although the arms 

 and pinnula3 are grooved, yet there are no grooves leading from 

 the bases of the arms to the mouth ; and it therefore becomes 

 probable that the ambulacral vessels of the arms and pinnulse do 

 not enter the body through that orifice. Indeed in a great many 

 species, as the mouth is situated in the top of a tube which is 

 sometimes longer than the arms and rises above them, it seems 

 impossible that they could gain access to the interior by that 

 route. Accordingly a more direct passage is provided. In a great 

 many species which have no calycinal grooves there is an aperture 

 at the base of each arm in which the groove of the arm terminates 

 I think that in such tpecies the ambulacral vessels, after descend- 

 ing from the extremity of the arms to the bases of the arms, pass 

 directly into the body through these apertures. I have therefore,, 

 in Decade III., proposed to call these the ambulacral orifices? 



The Decade contains descriptions of many new forms, some of 

 them, as is the case of the remarkable Blastoidocrinus car- 

 charicedens, worked out for the first time, and in a most able man- 

 ner, by the author of the Decade. These descriptions it is impos- 



