1914 202 F. A. Bather — Studies in Edrioasteroidea. 



suture they may just touch the post, oro-tegminal. It is not so 

 certain that these two plates are continuous elements. They seem to 

 he crossed by an obscure oblique suture at the level of the second 

 cover-plate of the adjoining grooves. It is not impossible that the 

 proximal portion of each of these plates may represent the proximal 

 cover-plate of the 1. ant. and r. post, grooves respectively. Those 

 are the grooves to which the supposed cover-plates would naturally 

 belong, in spite of the asymmetry involved. 



The tegmen of specimen B is so much more irregular and 

 asymmetrical that it cannot be described in detail. The r. and 1. ant. 

 oro-tegminals have the spear-head end. The proximal end of the 

 I. post, oro-tegminal is almost squeezed out of existence between the 

 contiguous grooves. The r. post, oro-tegminal is transversely divided, 

 and its proximal portion is nearly as large as the distal portion and 

 swells out to almost the same width. The post, oro-tegminal is 

 also divided transversely, and its distal portion is again split by 

 meridional sutures into three elongate plates. 



The Stem appears to have had a circular section, though in both 

 A and B it is slightly crushed. The diameters in B are 5*2 mm. and 

 3*75 mm., giving a mean of 4 - 47 mm. The lumen in B has diameters 

 circa 25 mm. and 1*75 mm., giving a mean of circa 1*9 mm. 



The columnars are irregular plates, differing considerably in height 

 and width, but tending apparently to form pentameres alternating 

 about more or less radially disposed sutures. In the post, interradius 

 of A the combined height of four such pentameres is 1*6 mm. ; these 

 alternate with three pentameres in r. post. IR having almost the 

 same height. In the 1. ant. III of B the combined height of three 

 pentameres is 2 - 7 mm., and in post. Ill two pentameres have a com- 

 bined height of 1*8 mm. 



There seem to be traces of spine-pits on the pentameres. 



Relations of Steganoblastus. 



The meanings of all the structures that have just been objectively 

 described will have to be discussed in a later paper. Here it is only 

 the immediate conclusions that can be drawn. 



First, the absence of brachioles, inferred from the lack of brachiole- 

 facets and the presence of large cover-plates, proves that Steganoblastus 

 is not a blastoid, not even one of the Protoblastoidea, as was at first 

 supposed. It also proves, if proof be needed, that it is not one of the 

 Cystidea Diploporita. 



Secondly, the structure of the subvective groove, with its floor- 

 plates and cover-plates, and its pores between the floor-plates, 

 is paralleled by Edrioasteroidea alone among Pelmatozoa, and in 

 that Class most closely by Fdnoaster, though there are minor 

 differences. 



Thirdly, the presence of a stem, and the enhanced pentamerism of 

 the thecal structures thereby induced, render it impossible to place 

 Steganoblastus in the Family Edrioasteridse. It has therefore been 

 necessary to establish for it the Family Steganoblastidse {Treatise, 

 1900, p. 209). 



