1914 167 F. A. Bather — Studies in Edrioasteroidea. 



The interradial plates are stout, those not far from the periphery 

 in E 15930 having a thickness of 1 mm. and over. They are tessellate, 

 with vertical sutures, but, as already described, dipping with, oblique 

 sutures under the radial floor-plates. There are no pores through or 

 between the plates. The surface in well-preserved tracts is coarsely 

 pustulate (PI. XI, Pig. 1). The pustules are distinct, and spring 

 from an irregularly reticular surface. E 16054, being a small and 

 presumably a young individual, shows the pustules rather faintly 

 and of smaller size than in the other specimens ; a large proximal 

 plate in the left anterior interradius has the pustules distributed 

 about 9 to 1'5 sq. mm. In E 15930, an individual of more than twice 

 the diameter, the pustules on a similarly placed plate run about 

 9 to 3 sq. mm. 



These pustules are not due to the breaking up of growth-lines by 

 radial stresses, but they may very well have been tubercles bearing 

 minute spines. Such spines, being very loosely attached, would 

 readily fall off after death, and would in any case escape observation 

 owing to their minute size. I have searched for them in the very 

 small amount of available material, but in vain, unless a tiny rod 

 ('8 mm. X "25 mm.) in the left anterior interradius of E 15930 may 

 possibly be one. 



The specimens of E. levis differ in having no distinguishable 

 pustules, a feature to which my attention was first directed by 

 Mr. Walter Billings. The exposed surface of these two specimens 

 has been somewhat worn (one had apparently been trodden on), and 

 this has exaggerated the smoothness. When other parts were freed 

 from their protecting matrix they presented a surface that might be 

 described as slightly vermiculate, or perhaps more accurately as 

 ' scrobiculate 



The Anus is well shown in specimen A (PI. X, Pig. 1). It lies 

 between the distal end of the right posterior groove and the bend in 

 the left posterior groove, and is surrounded by a number of small 

 plates, which must have lent greater flexibility to the test in this 

 region. Twelve of these plates meet round the actual opening, from 

 which the sutures between them radiate (PL X, Pig. 9). They are 

 not of equal length or width, and meet the smaller surrounding plates 

 quite irregularly. There is no imbrication. The area covered by 

 small plates rises up in a slight dome above the general level of the 

 interradius, but at its summit is again pushed in just round the anal 

 opening, possibly in consequence of post-mortem contraction. The 

 anal dome is not sharply defined on its right side, but seems continuous 

 with a general swelling of the thecal surface in that direction. The 

 rectum may have lain under here, and this, if so, would indicate that 

 the gut had a dextral coil. The similar appearances in E. buchianus 

 have received a similar interpretation from Professor Jaekel and 

 myself (cf. Study II, p. 199). 



In specimen B (PI. XI, Fig. 1) the periproctal plates are disturbed, 

 but the dome is discernible, as also the swelling on its right. In 

 the two specimens of E. levis the periproctals are numerous and 

 small, but do not appear to be elongate to any considerable extent. 



The Hydropore, or at least the thecal opening which I thus identify, 



