362 ON A NEW SPECIES OF AGELACRINITES. 
connected : more especially by the possession in common of a 
pyramidal orifice or, so called, anal-pyramid. It differs from the 
eystidean structure, nevertheless, in many important respects. The 
peculiar rays, the imbricating plates, the absence of a stem, for 
example, are essential points of difference. The imbrication of the 
plates serves to connect it, through the genus Protaster, with the 
Huryales or the Ophiurians; and the conformation of the rays, in 
certain species, appears to afford another link in support of this 
view. But is it not equally related to the Echinida? After a ~ 
‘eareful consideration of the subject, I cannot refrain from hazarding 
an opinion that the position of the mouth, as usually given, is 
erroneous. In several species, as in A. parasiticus and A. Kaskaski- 
ensis of Hall (Geology of lowa, Vol. 1., Part IL., Plate xxv.) the 
centre or origin of the rays is a simple dise or rounded tubercle— 
incontestably, no mouth: and hence we may fairly assume, that, in 
other species, the mouth must also be situated elsewhere. The 
question then arises as to the real nature of the pyramidal orifice. 
This-is usually looked upon either as an anal orifice, or as an ovarian 
aperture. Neither of these views is by any means certain, nor, 
indeed, apparently susceptible of proof. To consider this orifice 
as the mouth, however, appears a still less satisfactory conclusion. 
In the Crinoids proper, the true position of the mouth is still, 
_strictly, unknown. It is considered in some genera to be in the 
centre of the “ vault,’ or upper surface ; andin others to occupy an 
excentric position, as between two of the arms, &e. This latter 
view is unsustained by any proof, beyond the mere occurrence of an 
orifice at the points in question. The excentric orifice may or may 
not be the mouth. But if we omit these forms from consideration, 
and turn to those types. of Radiata, in which the position of the 
mouth is no longer doubtful, that organ, it will be seen, is invariably 
situated in the centre of the body, except in the Family of the 
Spatangide, the highest Family or natural group of the entire 
series. In the other Families of the HEcuinrpa, in the ASTERIDA, 
‘OpuivriDA, and other Orders in which the position of the mouth is 
truly known, the mouth is always central. This is evidently its 
normal position in the radiated type of structure, and one, conse- 
quently, that we should scarcely expect to see departed from, except 
in the case of those forms which stand at the higher limit of the 
series. Unless this view be adopted, we must almost necessarily 
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