ORDER V CRINOIDEA—ARTICULATA 175 
Actinometra, Miiller (Comaster, Goldf.; Phanogenia, Loven). Mouth 
eccentric or marginal; anus central or subcentral. Centrodorsal depressed, 
discoidal ; covered with a single (rarely a double) row of cirri, or sometimes 
altogether naked. Jura to Recent. 
Promachocrinus, Carp. Centrodorsal hemispherical or conical, and covered 
with numerous closely set cirri. succeeded by a single costal; with high 
distal faces and large muscle plates. Mouth central; ambulacra symmetri- 
cally disposed. Recent. 
Atelecrinus, Carp. Centrodorsal acorn-shaped, and bearing five double 
rows of cirri, those of each row alternating with one another and with those 
of adjacent rows. # separated from the centrodorsal by a complete circle 
of B. The first six or more orders of brachials devoid of pinnules. Recent. 
Thaumatocrinus, Carp. Calyx plates as in the preceding, but with the 
addition of five large interradials resting upon the basals, followed by small 
irregular pieces between the costals at four of the sides; the posterior 
interradial bearing a short, solid, jointed appendage. Ventral surface 
covered by a narrow band of perisome, and almost entirely occupied by five 
large, symmetrically situated orals. Mouth central; anus eccentric, and 
extended in a short tube. Arms five. Recent; found at a depth of 1800 
fathoms. 
Range and Distribution of the Crinoidea. 
With the exception of the Comatulidae, all recent Crinoids (Pentacrinus, 
Metacrinus, Rhizocrinus, Bathycrinus, Calamocrinus, Hyocrinus, Holopus) are deep- 
sea inhabitants ; and in many instances our knowledge of them is based upon 
but a few sporadic specimens. Of the Comatulidae, over 200 recent species 
have been described, the majority of which are found either in litoral zones, 
or in comparatively shallow water. 
Crinoids attained their maximum development during the Palaeozoic era. 
The three principal orders—the Larviformia, Camerata, and Fistulata—are 
wholly confined to the Palaeozoic rocks ; and with the exception of Marsupites 
and Uintacrinus, the same is also true of the Flexibilia. The Articulata, on 
the other hand, appear first in the Trias, and are represented continuously 
up to the present time. On this account Carpenter separated the Mesozoic 
and Cenozoic forms, under the term Neocrinoidea, from all earlier Crinoids, 
the latter being designated as Palaeocrinoidea. This distinction, however, has 
been shown to be largely artificial, and is now generally abandoned. 
Crinoids, as a rule, have but a very local distribution ; but in certain 
formations detached stem-joints and other fragments occur so profusely as to 
become of considerable rock-building importance; strata amounting to a 
number of metres in thickness are occasionally met with, which are almost 
wholly constituted of Crinoid remains. 
While the great majority of recent forms are deep-sea inhabitants, the 
Palaeozoic, on the contrary, often characterise shallow water deposits, and 
are especially numerous in the vicinity of fossil coral reefs. Of the Mesozoic 
Crinoids, the Eugeniacrinidae and Plicatocrinidae, whose remains are commonly 
associated with those of Hexactinellid and Lithistid Sponges, probably lived 
at considerable depths ; while, on the other hand, the Hncrinidae, Apiocrinidae, 
Saccocomidae, and Pentacrinidae, were undoubtedly shallow water forms. 
