384 Mr. C. Wachsmuth on the Internal and 
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surrounded by a furrow, as being the centre of radiation. It 
is located anterior to the proboscis, occupying a central or 
nearly central position. The middle of the space is occupied 
frequently either by a small opening or by a little cone imdi- 
cating an aperture leading toward the inner cavity; but in 
these casts the aperture is isolated, and there appears on the 
surface no connexion with the annular groove surrounding it. 
To understand this structure it becomes necessary to examine 
first some other casts from the same locality, mostly of Stroto- 
erinus and Actinocrinus, but also several of Batocrinus, though 
of different species from those which I have just described. 
These casts have no annular groove ; and the radiation, which 
is marked by elevated rounded ridges, almost like strings over- 
lying the surface, proceeds from a point in the centre where I 
noticed the little aperture in the former casts. The strings 
diverge toward the arm-bases in the same manner as the tubu- 
lar canals ; they are stronger toward the centre, decreasing in 
size with each bifurcation. That these ridges are remains of 
muscular cords is not probable, from the perishable nature of 
such organs ; and they are not their casts, or they should have 
left depressions in place of elevations. They can only be casts 
of passages which communicated with the central aperture, 
and which were evidently yet preserved when the siliceous 
mud, forming the casts, penetrated the body; but their cal- 
careous parts becoming in the course of time decomposed, a 
cast was left only of their inner channel; and this explains 
their string-like appearance. The little central aperture, lo- 
cated at the upper end of the vertical axis, occupied on the 
casts, and hence below the vault of these Crinoids, exactly the 
same position that the internal mouth of Antedon occupies at 
the peristome ; while the position of the string-like ridges (in 
case they represent passages, as I can hardly doubt) is analo- 
gous to that of the open food-grooves of recent Crinoids. 
The annular groove on the casts is probably an impression 
of the annular vessel, of which the calcareous parts have decom- 
posed. This organ, in the fossil state, heretofore only ob- 
served in the case of Actinocrinus Verneuilianus, existed un- 
doubtedly in all Crinoids. That we find no trace of it in 
some of the casts is no proof to the contrary ; 1t may have been 
sometimes composed of more perishable material and therefore 
not preserved, or situated at a greater distance from the vault 
and covered by the substance of which the casts were formed. 
2. The Ventral Furrow of the Arms. 
The arms of Paleozoic Crinoids manifest great diversity in 
outer form and structure, but are invariably provided with a 
