122 BRITISH PALEOZOIC ASTEROZOA. 



have been damaged and that originally the larger pieces were arranged in supra 

 marginal columns, while the smaller ones composed the radial row of ossicula." 



Unfortunately the original exposed apical piece has been lost ; I have, how- 

 ever, exposed the end of an arm of the Jermyn Street specimen and obtained 

 exactly the same arrangement as in Forbes's figure. The extremity of a " bent- 

 over " arm of the Dudley specimen is similar, but a more proximal portion of the 

 same arm showed a distinctly regular structure (Text-fig. 77), proving that Lepi- 

 daster is descended from a form with regularly arranged apical plates. Any 

 irregular arrangement of the ossicles is probably not due to post-mortem derange- 

 ment but to secondary changes of a similar type to those observed in Promo- 

 palmaster (p. 94) and Mesopalseaster Icetleijl (p. 103). This view is supported by 



go 



Text-fig. 77.— Plan of a portion of the apical surface of Lepidaster grayi (from the Birmingham 

 University Miiseum). I.M., infero-marginalia ; R., radialia; S.M ., supero-marginalia ? x 3. 



the text-figure, which shows that the breast-plate-shaped radialia are not always 

 closely touching but are separated occasionally by smaller plates — exactly the 

 stage figured for Promopalaeaster elizse (Text-fig. 52, p. 93). The changes are so 

 pronounced at the extremities of the arms that no regular arrangement is 

 discernible. The Dudley specimen also shows that the apical plates at the base of 

 the arm and those entering the disc are overlapping and very difficult to distinguish 

 from one another. In this respect they compare with the disc-ossicles of the oral 

 surface of the holotype, and may also represent a " senile " characteristic. 



Cross-Section (Text-fig. 78). — Arm xiii of the Jermyn Street specimen gives a 

 good view of a cross-section near the distal extremity. The large adambulacralia 

 and want of symmetry of the apical plates are noticeable, as also the reduced 

 ambulacralia. The figure should be compared with the cross-section of the arm of 

 a Urasterella given (Text-fig. 93, p. 148). In both cases it is very obvious that the 

 arm-cavity is much reduced. 



