V. Steganoblastus. 1914 201 



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

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

 ambulacrals, and gradually narrow as they pass, between the 

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

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

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

 a difference from the usual plan in that 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 

 customary and as they do in specimen B. 



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

 in the tegmen of specimen A. x 8 diam. 



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

 tapers gradually 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 

 general 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 



