388 Mr. C. Wachsmuth on the Internal and 
the tubular skeleton has been found in perfect preservation. 
There has been observed beneath the vault an annular vessel, 
constructed of plates similar to those of the radiating tubes, 
_ with small openings directed toward the radial sides of the 
specimen, with the alimentary canal passing through the inner 
space of the ring ; but its connexion with the surrounding parts 
was not preserved. ‘The position of the annular organ in the 
centre of radiation leaves but little doubt that it is the esopha- 
geal ring or centre of the ambulacral system. The great simi- 
larity in the construction of its plates, the presence of openings 
corresponding to the direction of the tubes, indicate most 
strongly that the tubes and the circular organ were connected, 
and that the ambulacral canal, which I recognized in the lower 
passage of the arms, communicated with the pores. But, as 
seen from the casts, there proceeded below the vault, from the 
arm-bases to the centre, another series of passages, which, 
passing the region of the annular vessel, united in the centre. 
I hold these to be a continuation of the food-grooves in the 
arms, which evidently, passing over the top of the circular organ, 
terminated within the central orifice. 
The position of the cesophageal ring seems at first sight to 
be not quite in harmony with recent nature ; this organ, which, 
in all Echinoderms with an external mouth, is attached to the 
inner side of the test, is located in Paleozoic Crinoids at a 
distance from the vault. However, considering that the aboral 
vault cannot be homologized with the oral skin of recent Cri- 
noids, and that only the tubular skeleton corresponds to the 
radiating passages connecting with the peristome, the vault 
thus forming a mere covering, we shall find the position of the 
circular organ perfectly harmonious with that of all other 
Echinoderms. 
I have mentioned already that there exists in the arm- 
groove of Cyathocrinus, beneath the tube and at the bottom 
of the furrow, another canal, as large as, or larger than the chan- 
nel of the tube, whose functions are unknown. It was, ap- 
parently through the bottom of the arm-openings, connected 
with the perivisceral cavity of the calyx, and may have served 
for several offices, containing perhaps also the cceliac canal. 
Dr. Schultze, in his Monograph on the Echinoderms of 
the Eifel, p. 17, gives a most excellent description of the arm- 
furrow in Cupressocrinus. He found two sets of plates covering 
the furrow like a roof, and asserts that the inner pieces could 
be turned back in the living animal. I had overlooked this 
in making out my descriptions; but it was pleasing and highly 
satisfactory to me to find that we both had arrived indepen- 
dently at the same conclusion. The construction of the arm- 
