Rofe-— Codonaster, &c. 251 
in the ‘ Third Decade of the Canadian Geological Survey,’ describes 
their ‘rhombs’ as ‘pores which penetrated through the plates of 
the body, and probably served as media of communication between 
the interior and exterior of the body, although the precise nature of 
their functions has not yet been ascertained.’ Figs. 10 and 11 are 
vertical and horizontal sections of the ‘ pectinated rhombs’ of Echino- 
encrinus armatus; and figs. 12 and 13 are like sections of the sum- 
mit of Codonaster: and it will be seen that in each case the ridges 
on the striated surface are the tops of a series of folds of a thin test 
or membrane; the alternate folds being so united at their ends as to 
form a series of long, but very narrow, sacs. In some specimens of 
Codonaster there is an appearance of a membrane, or peritoneum, 
lining the cup, and following round the outline of, and forming bags 
under, the above folds, as shown in fig. 14. 
From the construction of these striations on the face of Codo- 
naster and on the ‘pectinated rhombs’ of the Cystidea, may we, 
without assumption, suggest the possibility of their being respira- 
tory sacs, lined with cilia,* and constructed of a porous test, through 
which air from the water could pass by diffusion ? 
Beyond the form and construction of part of the cup, there ap- 
pears to be little in common between Codonaster and Pentremites ; 
and it must then be doubtful whether they should be left in the same 
family (Blastoidea), as the latter is apparently more nearly allied to 
the Crinoidea, whilst the construction of the ‘rhombs’ shows an 
affinity between the former and the Cystidea. Codonaster may 
possibly hereafter be found to be the representative of Cystidea in 
the Carboniferous series, or perhaps a connecting link between 
Crinoidea and Gystidea, having the cup of the one with the respi- 
ratory apparatus of the other. 
EXPLANATION OF PLATE VIII. 
Fig. 1. Horizontal section of Amphoracrinus, cut below the proboscis, which 
would be on the lower side of the figure. 
2. Side-view of Amphoracrinus: a, the opening, at the base of the 
arms, into the visceral cavity; 6, the passages in the shell from 
the base of the arms to the apex. 
. Cast of Actinocrinus tessellatus, Phillips. 
. Top-view of Cyathocrinus planus, Miller, The proboscis, on the 
lower side of the figure, is broken off. 
. Side-view of Rhodocrinus, with portions of the arms attached. 
. A pair of the arms of Rhodocrinus; enlarged about 4; showing the 
openings under them: a, opening with striz round it for the 
articulation of the fillet 6, shown under the other arm. 
. Section of Pentremites ellipticus, Sowerby; enlarged: a, the open- 
ing in the ‘lancet-plate.’ 
. Section of a pair of tubes and the ‘lancet-plate’ of Pentremites 
Jiorealis, Say ; much enlarged. 
. Section of a pair of tubes and the ‘lancet-plate’ of Pentremites 
imflatus, Sowerby ; much enlarged. 
Go ho 
(9) 
ive) 
* Cyclopedia of Anatomy and Physiology, vol. ii. p, 40, and vol. iv. p. 332. 
