VII. 198 F. A. Bather — Studies in Edrioasteroidm, 



matrix by the moat, and is itself bordered on its outer side by 

 a semicircular channel, which dips down on each side to join the 

 moat; just at those points, this channel is very nearly bridged by 

 projections from its enclosed matrix almost joining the proximal 

 prominences of the adjacent rays. Owing to the bridging and 

 overhanging of the matrix, it is impossible to obtain a satisfactory 

 wax squeeze of the channels ; but, translating the appearances into 

 the original stereom structures, we infer that the mouth was central 

 and roughly five-lobed, widest on the posterior side, and that it 

 was surrounded by a stout ring of stereom, over which the food- 

 grooves passed. This latter structure may possibly be that described 

 by Salter (op. cit., p. 291) as "a great thickening of the oral 

 ossicles, just within the mouth." The proximal or adoral pores 

 were connected with one another above this stereom ring, but below 

 the outer theca, so as to form a closed ring-canal (hydrocircus) 

 around the mouth. In the posterior interradius was a madreporite 

 or hydropore-plate, the inner surface of which formed a semicircular 

 projection for the attachment of the upper end of the stone-canal. 

 This was more or less directly connected with the ring-canal. The 

 existence of pores along the radial grooves almost certainly implies 

 the presence of podia, as well as of perradial water- vessels connecting 

 the latter with the ring-canal. But the specimen does not afford 

 satisfactory evidence as to the position of the perradial vessels. 



The shape of the Interradial Areas has been figured by Forbes 

 (op. cit., pi. xxiii, fig. 5), but the arrangement of the plates thus 

 represented, though not ridiculous, is imaginary so far as details are 

 concerned. His drawing, however, presents a certain resemblance 

 to the left anterior interradial area, here refigured (Fig. 5). This 



Fig. o. / LA^ 14 j\ Fig. 6 



Fig. 5. — Arrangement of plates in left anterior interradius. Nat. size. 



Fig. 6. — Arrangement of plates in upper part of posterior interradius. Nat. size. 



st.c. depression caused by stone-canal, mes. depression perhaps caused by 



mesentery. 



shows the marks left by the plates pretty clearly, and indicates 

 that they were irregular polygons of various sizes, apparently not 

 imbricate. The only regularity visible in their arrangement here 

 is a band of plates bordering the right side of the area, and 

 passing across it at the lower edge of the theca, while another less 

 regular band runs parallel to, and on the inner or left side of, this 

 outer one. Down to and including these bands, there were 36 plates 

 in the left anterior interradial area. The greatest width of this 



