ORDER v CRINOIDEA ARTICULATA I 7 :> 



Adinometra, Muller (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. 



Pr&machocrinus, Carp. Centrodorsal hemispherical or conical, and covered 

 with numerous closely set cirri. 11 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 altcri&ting with one another and with those 

 of adjacent rows. R 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 literal zones, 

 or in comparatively shallow water. 



Crinoids attained their maximum development during the Palaeozoic era. 

 The three principal orders the Larmformia, Camerata, and Fistulata are 

 wholly confined to the Palaeozoic rocks; and with the exception oiMarsupites 

 and Uintacrinus, the same is also true of the FlexiUlia. 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, iheJEncrinidae, Apiocrinidae, 

 Saccocomidae, and Pentacrinidae, were undoubtedly shallow water forms. 



