BIONOiMIC CHARACTERS OF ECHINODERMS 103 1 



were distinct from the Mesozoic and recent forms. The modern 

 Chilopoda date from the Tertiary; the Diplopoda from the Cretacic. 



ECHINODERMATA. 



Cystoidea and Blastoidea. These classes are entirely extinct, 

 being confined to the Palaeozoic. They were undoubtedly marine 

 organisms like all the echinoderms. 



Crinoidea. The crinoids are without exception marine organ- 

 isms, though Anted on rosacea has been taken m water containing 

 only 25 permille of salts, or nearly a third less than in normal sea- 

 water. The majority of crinoids belong to the sedentary benthos, 

 being anchored or attached to the sea-bottom either by a stem or 

 by the base of the calyx. Antedon must be classed with the vagrant 

 benthos for, although it ordinarily rests on the sea-bottom or other 

 stationary objects of support, it is able to walk about on the bottom 

 by means of its arms ; and also to swim with graceful movements 

 through the water. Planktonic crinoids appear to have existed in 

 the Mesozoic seas ( Saccocoma, Uintacrinus), and, as already noted, 

 Walther has furnished evidence which indicates that some of the 

 stemmed Pentacrini of the Lias led an epiplanktonic life, grow- 

 ing attached to floating timbers with which they were carried about, 

 calyx downward. 



Kirk (18) has recently brought forward evidence to show that 

 many Palaeozoic as well as later crinoids separated from their stems 

 late in life and assumed secondarily a planktonic existence, the 

 crowns floating away, while the dead stems remained behind to 

 separate into their component ossicles and form a bed of crinoidal 

 limestone. 



The bathymetrical distribution of tlie modern crinoids ranges 

 from shallow water to 2,000 fathoms, rarely more. One species of 

 Antedon {A. abyssicola, Carp.) has been obtained at a depth of 

 2,900 fathoms, but most of the species of this genus live in shal- 

 low water. A. loveni. occurring in three to four fathoms. This 

 genus is perhaps the most cosmopolitan of the modern crinoids, its 

 geographic range being between eighty degrees northern and fifty- 

 two degrees southern latitude. The following modern stalked cri- 

 noids have been obtained in less than ninety fathoms of water 

 (Walther-29:i'p6'- ?oo) : 



Eudiocrinus indh-isus Semp., 30 fathoms (54 meters). 

 Metacrinus rotiindus Carp., 70 fathoms (128 meters). 



