1914 169 F. A. Bather — Studies in Edrioasteroidea. 



and probably the same number, not more, in A. In E. buchianus eleven 

 such plates were counted, but the general shape and arrangement are 

 the same in the two species. The inner margin of each frame-plate 

 in E. bigsbyi is straight or concave, not convex as in E. buchianus. 

 I have not observed on them any sign of tubercles or pustules, such 

 as appear to have existed in E. buchianus. 



The Central Area, in all specimens where any portion of it can be 

 seen, is darker in colour and irregularly wrinkled (PI. X, Fig. 11). 

 It was doubtless covered by a flexible integument, filled with minute 

 plates, which it has been possible to observe, though not clearly to 

 photograph, in some tracts of specimen C (Plate XIII) and in E 16172 

 and E 15930. This scaly skin was attached to the frame-plates, and 

 may as a rule have spread over them to some extent, especially at the 

 sutures between them. The minute plates were tan gentially elongate, 

 and when closely pressed together, as in the folds, tend to project and 

 to imbricate. 



The adapical face of E 15930 (PI. XIV, Fig. 1) differs from that of 

 all other specimens observed in the apparent absence of a frame : the 

 plated integument seems to stretch right up to the peripherals. 

 In the region that should be occupied by the frame there are, however, 

 appearances as though the integument had been thrown into raised 

 circular or crescentic folds, each bounding a strongly pustulate floor. 

 It may be that this floor is formed by the fusion of small plates, or 

 that it indicates a frame-plate underlying the plated integument. 



In cleaning away the matrix, it was peculiarly interesting to 

 discover in these species the lobed central evagination, which I first 

 made known in E. buchianus. Its pentagonal shape is not so obvious 

 here. In A it is roughly triangular, with a short base in the left 

 anterior interradius, and two long sides directed to a distinctly folded 

 apex in the right posterior radius. One of these sides may be 

 regarded as containing the lobes of the right anterior and right 

 posterior interradii, and the other those of the posterior and left 

 posterior interradii. In C (Plate XIII) the irregular lobate edge 

 of the posterior half of this evagination is clearly seen, and we are 

 perhaps justified in distinguishing the lobes of the three posterior 

 interradii. 



Prolonged preparation and repeated examination of the area 

 surrounded by the lobes in A, C, and E 16172, have convinced me 

 that there was no central opening of a permanent nature, such as 

 E. Billings mentioned as apparently present (1854, p. 272). Neither 

 is there evidence for pores of any kind in any part of the adapical 

 face. It is perhaps hardly necessary to add that there is no sign 

 of any stem or root, unless the central lobed region be regarded as in 

 some sense the homologue of a stem. 



Discussion of the physiological and morphological meaning of the 

 structures herein described is reserved until, in a forthcoming Study, 

 the structure of Steganoblastus shall have been redescribed. At 

 this point, however, the distinctive features of the genus Edrioaster 

 and of its four known species may be resumed in the following 

 diagnoses. 



