298 THE MEDALS OF CREATION. Crap. VIII. 
for the transit of vessels that supply an infinite number of 
delicate simple tentacula, composed of extremely minute cal- _ 
careous ossicula, as in the other Crinoidea, but not subdivided 
as in the Pentacrinites and Encrinites. 
_ These articulated tentacula are arranged close together in — 
longitudinal rows on the ambulacral spaces ; there being two 
rows, each consisting of fifty tentacula, on every space. They — 
are directed upwards towards the vertex of the receptacle, — 
and appear to be the instruments for the capture and con- 
veyance of food to the mouth.* 
There are several species of Pentremites, some of which 
swarm in the cherty limestones of Kentucky. Mr. Say, to 
whom we are indebted for the first satisfactory investigation 
of these fossils, mentions that such is their abundance, that 
he has observed, on a piece of rock not larger than three 
inches by two-and-a-half, above twenty specimens lying in ~ 
relief. 
CystipEA.—In the ancient fossiliferous strata there occurs — 
a remarkable family of crinoideans, which is supposed to be — 
restricted to the palzozoic ages ; these fossils have been named — 
by Von Buch, Cystidee, from the body of the animal being ~ 
wholly inclosed in a cyst, or box. The receptacle is of a — 
spherical form, and composed of polygonal plates, articulated — 
to éach other; it has distinct apertures for the mouth, vent, 
and oviduct; the orifice of the latter is closed by valves. It 
has a short neue, but no arms have been discovered, and 
the Cystidez are generally described as Crinoids without 
appendages of this kind. But in some members of this — 
group, there are not only arms and tentacula, but likewise 
certain organs connected with the plates, which Prof. HE, — 
Forbes terms, “ pectinated rhombs,” the functions of which — 
are not obvious. The arms more closely resemble those of 7 
* See Dr. Fred. Roemer on jointed tentacles found on the ambu- — 
lacral spaces of Pentremites, “Geol. Journal,” vol. v. p. 8. 
