93 



There are ten arms ; the test is very thick ; the ambulacral channels con- 

 verge to the central point (c) but do not quite reach it ; the mouth (mv) 

 is about half way between the center 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 tunneled, as it were, through the substance of 

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

 space (c). 



Fig. 52 — is a plan of the ?ummit of the widely known and remarkable 

 fossil Carijocrinus 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 UcJiinus, and can only be seen in well preserved and clean spe- 

 cimens. 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 (mv) is valvular, composed of from five to eight or ten plates, 

 and is always situated near the margin between 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 destitute of 

 that aperture. 



Caryocrinus is a genus which seems to form a connecting link between 

 the Crinoidea and the Cystidea. By examining numerous well polished 

 sections I find that the structure of the respiratory areas is the same (in 

 general plan) as that of the genera Glyijtocystites, Pleurocystites and 

 Echinoencrinites^ as will be shown further on. The arms are also 

 arranged in three groups as in Sphceronites and Ilemicosmites, while the 

 mouth is valvular. On the other hand, the long cylindrical column and 

 the arrangement of the arms around the margin, with the ambulacral 

 pores at their bases, are crinoidal characters. 



In addition to the above, the following species may be referred to, as 

 examples of Crinoids with the mouth separate from the centre of the radial 

 system. 



Amphoracrinvs tesselafus (PhillipsX— Figured by J. Rofe, Esqr. Geol. 

 Mag., vol. ii, p. 8, f 3. The figure represents a cast of the interior of 

 the vault showing the five ambulacral grooves in relief. The mouth is 

 situated in the angle between the two anterior grooves. 



Slrotoerinvs perumhrosus (Hall, sp.\— Figured by Meek and Worthen 



