REPORT ON THE GENUS ORBITOLITES. 37 



The examinatiou of a large number of specimens of this type, which show every gra- 

 dation between the reguUxr smooth discoidal form (fig. 3) and the strongly " laciniate " 

 forms represented in figs. 6 and 7, has satisfied me that the latter type has no claim to be 

 distinguished specifically. Both in kind and degree the peripheral " laciniation " is 

 subject to the widest extremes of individual variation ; and there is neither constancy 

 nor regularity of disposition in the outgrowths from the inner portion of the disks, those 

 of the two sides of the same disks being generally quite dissimilar. It may be questioned 

 whether they have even a greater claim to be distinguished as constituting a well- 

 marked variety than have, for example, the deeply plicated specimens of Waldheimia 

 australis, which are found adherent to the same blocks of stone as the smooth, with 

 a series of intermediate forms establishing a gradational transition from the one to the 

 other. ^ 



Reparations. — There seems no more limit in this species to the reparative power than 

 in those " simple " types in which its operation has been previously described ; an entirely 

 new disk, perfect in every part except its centre, being producible from a small fragment 

 broken away from the margin of an older one, as shown in PL VIII. fig. 10, — which is 

 the exact counterpart to PI. I. fig. 7, though representing a much larger and older disk of 

 this "complex" type, under a comparatively low magnifying power. So, in PI. VIII. fig. 2, 

 we have the exact counterpart to PI. I. fig. 6 ; the former, which represents a repaired 

 disk of Orhitolites complanata nearly half an inch in breadth, showing that a fracture 

 across its diameter when about half its present size did not in the least interfere 

 with its subsequent growth, and that, from the very first, new annuli were formed all 

 along its fractured edge, as around its normal margin ; so that, except in the modification 

 of shape produced by the loss of half the earlier portion of the disk, no departure from 

 the normal type is discernible. In fig. 8 the proportion of the disk lost by transverse 

 fracture is smaller, so that the growth of peripheral annuli aU round has more nearly 

 restored the circular form. In fig. 6 this restoration has been yet more complete, though 

 the early loss of a considerable proportion of the disk has given the nucleus an excentric 

 position. In fig. 4 there seems to have been a marginal breaking away of several 

 portions of the disk, leaving a very irregular outline ; the broken portions have been 

 fiUed-in, and the circular form has been almost exactly restored. In the specimen repre- 

 sented in fig. 9 a sort of notch has been cut out from the margin of an advanced disk, 

 and this has been fiUed-in by an extension of the later-formed peripheral annuli. It is 

 obvious that if the growth of this disk had proceeded much further the notch would 

 have no longer shown itself at the margin. In the disk represented in fig. 5 the more 

 considerable loss has been less completely repaired, the new growths from the two sides 

 not having as yet met : but it is obvious that the addition of a few more peripheral 



1 See pi. i. of the Jlonograph of the genus Terebrahila, in Lovell Reeve's " Conchologia Iconica." The original 

 of this plate— a block brought by Prof. J. Beete Jukes from Port Jackson— is in the British Museum. 



