280 EHE CANADIAN NATURALIST. [Sept. 



the remains of the thin partitions which either separated them or 

 to which the vessels were attached. They do not run directly 

 toward the mouth, as they would do if that organ were the centre 

 of the ambulacral system, but to the small space (c) behind it, 

 where there appears to have been situated a vesicle or some other 

 apparatus, to which all of them were united. Whatever may 

 have been the structure of this central organ, from which the five 

 main grooves radiate, it no doubt represented the annular vessel 

 of the recent Echinodermata, to which Prof. Thompson alludes. 



Fig. 2 — represents the structure of an AmpTioracrinus, from 

 the Carboniferous rocks of Ireland, — precise locality and species 

 not determined. There are ten arms ; the te?t is very thick ; the 

 ambulacral channels converge to the central point (c,) but do not 

 quite reach it ; the mouth {mv) is about half-way between the 

 centre and the margin. In this Crinoid it is perfectly impossible 

 that the mouth can be the centre of the radial system, because 

 the two anterior passages, between which it is situated, are for 

 their whole length tunnelled, as it were, through the substance of 

 the plates, and only penetrate downward into the interior at the 

 central space (c.) 



Fig. 3 — is a plan of the summit of the widely known and 

 remarkable fossil, Caryocrinus ornatus, (Say.) In this species 

 there are only three, instead of five, groups of arms. In large 

 individuals there are from twelve to twenty free arms (but always 

 arranged in the three groups) with a small pore at the base of 

 each. This pore is about the size of the ovarian pore of an 

 Echinus, and can only be seen in well preserved and clean speci- 

 mens. The ambulacral grooves have not yet been observed, but 

 their course is indicated by three low rounded ridges, which may 

 be seen, in some specimens, radiating from a large heptagonal plate 

 situated at (c). The mouth (jnv) is valvular, composed of from 

 five to eight or ten plates, and is always situated near the margin 

 betwen the two anterior groups of arms. With the exception of 

 the ambulacral pores there is positively no other aperture in the 

 summit of Caryocrinus. If it be true that the mouth of an 

 Echinoderm must be always situated in the radial centre, then 

 Caryocrinus, and also nearly all the paleozoic genera were desti- 

 tute of that aperture. 



Caryocrinus is a genus which seems to form a connecting link 

 between the Crinoidea and the Cystidea. By examining numer- 

 ous well polished sections, I find that the structure of the 



