146 ECHINODERMATA—PELMATOZOA SUB-KINGDOM III 
Ollacrinus, Cumberl. — (Gilbertsocrinus, Phill. ; Goniasteroidocrinus, Lyon and 
Cassed.) Agreeing with Rhodocrinus in the structure of the calyx below the 
arms, but readily distinguished by the so-called pseudobrachial appendages, 
and by the size and disposi- 
tion of the arms. Above 
each distichal is a round 
ambulacral opening (ten in 
all), through which the am- 
bulacra of the arms conduct 
into the calyx. From above 
each of these openings spring 
two tufts of small, branching, 
pinnule-bearing arms. These 
are either folded over the 
tegmen, or they bend down- 
wards with the ventral side 
exposed to view, the pinnules 
being directed upwards. Ten 
tubular appendages extend 
outwards and downwards 
from the upper margin of 
the calyx. In the American 
Rhipidocrinus crenatus, Goldf. sp. Devonian; Gerolstein, Hifel. Ce i: : 
A, Perfect crown, of the natural size (after Schultze). B,Tegmen, SP€C1lesS these are united later- 
with eccentric anus. C, Interior view of the base, showing the five . a7 ace ~ ic 
IB, two of the B, and one R. D, Column. £, Face of stem-joint. ally In pairs for some dis- 

Fic. 248. 
tance ; but in the European 
ones they are separated. One species in the Hamilton Group of New York ; 
the remainder Sub-Carboniferous ; North America and Europe. 
Lyriocrinus, Hall. Calyx depressed ; plates smooth or finely granulose. 
Tegmen almost flat, composed of a large number of small plates. | Anus 
eccentric ; not extended in an anal tube. Arms ten, strong, simple, biserial. 
Confined to the Niagara Group of North America. 
Rhipidocrinus, Beyrich (Fig. 248). Calyx cup- or urn-shaped, with a more 
or less flattened or concave base. Plates of the dorsal cup heavy, and highly 
ornamented. JB five, small, forming a pentagon. # five, equal; & and 
axillary costals pentagonal. First J? large, heptagonal. Tegmen low, com- 
posed of an immense number of small thick plates, irregular in their arrange- 
ment; anus eccentric. Arms given off from calycular appendages, and 
composed of wide transverse pieces, which bear at intervals on alternate sides 
biserial, pinnule-bearing armlets. Column round, heavy ; axial canal pentalo- 
bate. R. crenatus, Goldf. sp. Middle Devonian ; Eifel. 
Thylacocrinus, Oehlert. Resembling Lyriocrinus, but the calyx more elongate. 
IR and interdistichals profusely developed. Arms numerous, heavy, biserial, 
not branching in the free state. Devonian; France and North America. 
Diamenocrinus, Oehlert. Devonian; Manche (France) and Germany. 
Family 8. Melocrinidae. Zittel (emend. W. and Sp.) 
Base monocyclic.  Basals three to five ; radials laterally in contact, not enclosing 
an anal plate.  Interbrachials frequently separated by supplementary anals. Ordo- 
vician to Devonian. 
