Dr. F. A. Bather — Studies in Edrioasteroidea. 201 



only five plates, which have already been alluded to as the oro- 

 tegminals. These abut by their distal broader ends on the inter- 

 aiubulacrals, and gradually narrow as they pass, between the 

 converging and narrowing series of cover-plates, towards the oral 

 pole. As is usual in Pelmatozoa, only three of them meet there : the 

 posterior and the right and left anterior. There is, however, 

 a difference from the usual plan in tliat these three can scarcely 

 be said to meet in a triradiate suture ; but the posterior plate passes 

 between the other two and with its pointed apex actually touches the 

 proximal cover-plate of the anterior radius, so that in this individual 

 the two anterior oro-tegminals do not touch one another as is 

 customarj' and as they do in specimen B. 



/ cover- 

 / plates 



Fig. 6. Steganohlastus ottawaensis. Exact drawing of the sutures 

 in the tegmen of specimen A. x 8 diani. 



These three oro-tegminals have the same general shape. Each 

 tapers gradiially as the subvective grooves bounding it converge, 

 then, as the grooves are rounded off, it expands, and again tapers 

 rapidly to a sharp point, thus resembling a spear-head. Each of 

 these three plates appears to be one continuous element, from the 

 pointed apex to the broad straight base. 



The two other oro-tegminals, the r. and 1. post., are of the same 

 genei'al shape, except that they do not end in a spear-head, but in an 

 oblique suture, abutting on the adjacent side of the spear-head of the 

 r. and 1. ant. oro-tegminal respectively. At the extreme end of this 



