1072 NOTES ON AUSTRALIAN FOSSILS, 



In Actinocrinus the basal disc has three plates forming an 

 hexagon, and the subdivision of these plates will form six 

 basals instead of five, but then the anal plate comes in as shown in 

 the ' Revision ' (pi. XV. fig. 4) requiring two plates, which may be 

 considered equivalent to one, for its support, and the structure 

 remains in principle the same as in the foregoing cases. Let 

 us now consider forms provided with underbasals. 



In forms like Cyathocrinus, Rhodocrinus (fig. 2), etc., in 

 which the ring of plates next to the stem is formed of five 

 segments, these plates are radially situated as underbasals, while 

 the next ring is composed of the five basals interradially situated. 

 In most of the Ichthyocrinida the lower ring is composed 

 of three plates, but then, if we divide them by sutures into 

 five, about equal plates, these five will be radially situated as 

 underbasals, and exactly equivalent to the corresponding set of 

 plates in Cyathocrinus, etc. 



The authors of the ' Revision ' continue as follows : — 



"It is now a very important fact that these two rings of plates 

 — the first radials and the interradial set of plates next below 

 them — are the only ones which are found in all crinoids from the 

 earliest geological ages to the present time. It thus appears that 

 the evidence derived from the embryology of the Pentacrinoid, 

 and the observed mode and order of development in the Palaeo- 

 crinoids during individual life, is fully and beautifully confirmed 

 by the geological history of crinoids." 



" All this evidence seems to us (Wachsmuth and Springer) to 

 be conclusive, and to prove satisfactorily that the two rings of 

 plates regarded by Carpenter as genitals and oculars, are the 

 fundamental parts in the aboral side of the calcareous skeleton, 

 and that the subsequent orders of radials and interradials are to 

 be considered as supplementary to them, and as the products of 

 growth in the individual and development in geological time." 



( ' Our conclusions being thus in harmony with Dr. Carpenter's 

 views, we think it both logical and expedient to adopt his terms, 

 and call the first ring of plates below the radials basals in all cases, 

 and the second ring below, or the proximal plates when there are 



