CLAss III CRINOIDEA 183 



(Comatulids), the ränge for the stalked species being from 5 to 2325 

 fathoms. The great majority of the existing types are littoral and snblittoral, 

 oidy a few descending into'the abysses. A very large nnnib(3f of species, 

 many genera, and several families are confined to the East Indian region, while 

 all the species and genera occurring outside of that region have close relatives 

 within it. Most forms are highly gregarious, occurring in great numbers 

 together, these masses being often composed, in the East Indies, of twenty or 

 more different species, but a few appear to be more solitary in habit. As a 

 rule the Eecent forms are very local, and, though they may be found in certain 

 very restricted areas in large numbers, and may have a very wide geographical 

 ränge, it is comparatively seldom that one meets with them. 



Fossil Crinoids also appear to have been gregarious in habit, and their 

 remains are frequently found commingled with those of reef-building corals 

 in Paleozoic strata. Owing to the extremely delicate Constitution of many of 

 the skeletal parts, and the looseness with which the plates and segments are 

 united, the Crinoid organism is by no means favourably adapted for preserva- 

 tion in the fossil state. Perfect crowns are of comparatively rare occurrence, 

 calices more frequent ; but, on the other hand, detached joints of the stem 

 and arms are often very abundant, and form beds of considerable thickness. 

 Orinoidal limestones of greater or lesser extent are met with in numerous 

 formations from the Ordovician to the Jura ; those of the Carboniferous and 

 Muschelkalk (Trochitenkalk) being especially characteristic. 



Classification. — The first attempt to construct a Classification of the 

 Crinoids was that of J. S. Miller in. 1821. Four groups differing in the form 

 and mode of union of the calyx plates were distinguished by Miller as 

 follows : C. articulata, semiarticulata, inarticulata and coadunata. The Classi- 

 fication of Johannes Müller, in 1841, was based upon a number of difFerential 

 characters, such as the articular or close suture of the radials, the thick- 

 ness of the calyx plates, the mobility of the arms, and the plated or 

 cbriaceous character of the ventral disk. Two principal groups were 

 recognised : Articulata and Tesselata ; while a third (Costata) was constructed 

 for the reception of the unique genus Saccocoma. T. and T. Austin and 

 F. Roemer adopted the untenable divisions of Stalked and Unstalked 

 Crinoids. 



The importance of Wachsmuth and Springer's investigations on the 

 structure of the calyx, especially of the tegmen, and on the orientation of 

 the stem and its canals in monocyclic and dicyclic forms, cannot be over- 

 estimated. Two groups were proposed in their Classification of 1879 : 

 Palaeocrinoidea and Stomatocrinoidea ( = Neocrinoidea, Carpenter) ; groups which 

 correspond in the main with the Tesselata and Articulata of Johannes Müller. 

 This Classification was subsequently abandoned, and a new one suggested for 

 it in 1888, afterwards more fully defined in their monograph on the North 

 American Crinoidea Camerata in 1897, in which three principal grand 

 divisions, or Orders, were recognised, which were believed to include sub- 

 stantially all Crinoids, fossil and recent, viz.: Camerata, Inadunata and 

 Articulata. 



Jaekel in 1894 proposed two Orders, Cladocrinoidea and Pnitnmnmdea, 

 the former containing only the Camerata (W. and Sp.), and the Int t er ;ill the 

 rest. Bather in 1898 divided the Crinoids according to the composition of 

 the base into two subclasses, Monocyclica and Dicyclica, recognising for the 



