2] I 



BRITISH PALEOZOIC ASTEROZOA. 



Schuchert's drawing shows the adambulacralia not meeting above the radial 

 line. In I). 331 andD. 332 the adambulacralia meet across this line and completely 

 close the groove. This may be simply due to a greater contraction of the "walls of the 

 groove at the time of entombment, or it may have some slight specific value (see 

 below). The adambulacralia of the American species are said to be very convex. 

 Those of the British form are rounded but not strikingly convex. The inner 

 sides of the adambulacralia are stated by Schuchert to bear tufts of short 

 blunt spines. 



Apical Surface (PL XV, fig. 1 ; Text-figs. 150, 151).— The American form has 

 " abactinal areas of rays and disc composed of very numerous, small but 

 irregularly sized, sub-quadrate or diamond shaped, slightly pustulose plates. The 



,,-MA.P. 



Text-fig. 153.- Lino drawing of Sehuchertia laxata (combined from 1> . :t::i and D.332). Ad., adambulacralia- 

 I.M., infero-marginalia ; M.A.P., mouth-angle plates; 0., odontophor. x 5. 



arrangemenl is mainly in quincunx, but a columnar arrangement is also noticeable." 

 Isolated plates of this form are shown in Text-fig 150. The drawing of the 

 British form given. Text-fig. 151, is very good evidence of the identity of the two 

 sets of material. The ossicles are distinctly more irregular than those of S. stellatn. 

 The distal portion of the arm in the drawing shews only three rows of plates. 

 At leasl two more were undoubtedly present originally, but are now represented 

 only by •(•uttered plates. The median row shows a tendency to differentiate into 

 breast-plate-shaped radialia. 



Measurements.— J). 332 gives the following approximate measurements: 

 R : r : : 1/ nun. : 6 mm. The other specimens were probably of approximately 

 the same size. 



Schuchert states thai the best American specimen "measure's : R = is mm.. 



