707 



Tllli: KECENT CRINOIDS OF AUSTRALIA — CLxXUK. GG3 



A few other specimens are from scattered localities ; but some 

 of tliese are of very exceptional interest, and cannot justly be 

 omitted from consideration. They are therefore included with 

 the above. 



From a palaeontological point of view the study of the recent 

 Crinoids is of more importance than tliat of any other animals so 

 far as the marine deposits are concerned. There are three 

 reasons for this : — 



(1). The Crinoids are animals of the greatest antiquity and 

 theii- palteontological record therefore shows a succession of forms 

 none of whicii depart very widely from the general type ; 

 developmentally speaking the lapse of time since the first vestiges 

 of crinoidal remains is infinitesimal, and the Crinoids of the 

 several past horizons can only logically be considered as consti- 

 tuting so many separate zoogeographic areas, all of equal value, 

 and all equal in terms of phylogenetic development to the zoogeo- 

 graphic areas of to-day. In fact one is almost justified instating 

 that the phylogenetic perfection of the Crinoids is in inverse pro- 

 portion to tlieir age as we know it from their position in the 

 rocks, so great has been their .specialization in the past, and a 

 phylogenetic tree beginning with the Crinoids of the present day 

 and ending with those of the Cambrian would have just as much 

 to recommend it as one following the so-called development of 

 the class from Cambrian times to the recent epoch. Thus, the 

 past history of the Crinoids may be said to be a radial, instead of 

 a linear, succession of types, each one of which takes a position 

 on or near the circumference of a circle, and all of which are 

 nearly equidistant from the two or three indicated primitive 

 types which occupy its centre. 



(2). The Crinoids are securely attached by a stem and root, 

 and thus immovably fixed, or attach themselves to various objects 

 by means of their cirri, remaining as a rule stationary for life ; 

 the young are always fixed. As we know it, the free larval 

 existence is passed chiefly within the vitelline membrane attached 

 to the pinnules of the parent, the actual free swimming stage 

 not being of more than forty -eight hoars' duration. Thus, of all 

 marine animals the Crinoids are the most nearly strictly sessile. 

 This I'enders them most valuable aids in tracing out the funda- 

 mental facts of the distribution of marine animals, both past and 

 present, for it reduces to a minimum the effect of ocean currents 

 upon them, and, since individual species are strictly limited in 

 their thermal and Ijathymetric range (especiall}' in the former), 

 it results in the interposition of certain barriers to their distri- 

 bution more or less inoperative in the case of other animals, 

 including the other Kchinoderras. Chief among these barriers 

 are deep channels of considerable width which the littoral and 



