BRYOZOA AND GRINOIDEA.—MOLLUSCA. 
433 
Bryozoa and Crinoidea. — Of the Bryozoa^ the prevailing 
forms are Fenestella^ Hemitrypa^ and Polypora^ and these 
often form considerable beds. Their net-like fronds are easi¬ 
ly recognized. Crinoidea are also numerous in the Mount- 
Fig. 478. 
Cyathocrinus planus^ 
Miller. Body and 
arms. Mountain 
Limestone. 
Cyathocrinus caryocrinoides, M‘Coy. 
a. Surface of one of the joints of the stem. h. 
Pelvis or body; called also calyx or cup. 
c. One of the pelvic plates. 
ain Limestone (see Figs. 478, 479), two genera, Pentremites 
and Codonaster^ being peculiar to this formation in Europe 
and North America. 
In the greater part of them, the cup or pelvis. Fig. 479, 
is greatly developed in size in proportion to the arms, al¬ 
though this is not the case in Fig. 478. The genera Poteri' 
ocrinus^ Cyathocrinus^ Pentremites^ Actmocrinus^ and Platy- 
crinus^ are all of them characteristic 
of this formation. Other Echino- 
derms are rare, a few Sea-Urchins 
only being known : these have a 
complex structure, with many more 
ptates on their surface than are seen 
in the modern genera of the same 
group. One genus, the Palcechmus 
(Fig. 480), is the analogue of the 
modern Echinus^ but has four, five, 
or six row^s of plates in the inter- 
ambulacral region or area, whereas the modern genera have 
only two. The other, Archmocidaris^ represents, in like man¬ 
ner, the Cidaris of the present seas. 
Mollusca. — The British Carboniferous Mollusca enumer¬ 
ated by Mr. Etheridge* comprise 653 species referable to 86 
genera, occurring chiefly in the Mountain Limestone. Of 
* Quart. Geol. Journ., vol. xxiii., p. 674, 1867. 
19 
Fig. 480. 
Palmchinus gigas, M‘Coy. 
Reduced one-third. Mountain 
Limestone. Ireland. 
