F. A. Bather — Studies in Edrioasteroidea — //. 203 



Edrioaster Bigshyi, 1858. In the list on p. 262 of the same work 

 it is actually called " Edrioaster Buchii (Agelacrinus, Forbes)." The 

 same is the case in Etheridge's revision of Salter (pp. 481 and 395). 

 Salter's opinion is abundantly justified not only by the details of 

 the present paper, but by the new facts concerning Edrioaster 

 Bigshyi, which will form the subject of the next study. To that it 

 is better to postpone the diagnoses of the genus and of the present 

 species. 



EXPLANATION OF PLATES VIII, IX, and X. 



Edrioaster Buchiaxus. 



[AU the figures are from the tj'pe-specimea iu the Museum of Practical Geology, 

 except PI. X, Fig. 3, which is troni a fragment associated with it. Plates VIII 

 and IX are based on photographs by Mr. J. Green ; the figures of Plate X are 

 drawn directly from the specimens or from wax squeezes thereof. The figures of 

 Plates VIII and IX are magnified two diameters ; those of Plate X are enlarged 

 to the extent stated under each. Difiiculties of lighting have rendered impossible 

 a rigorous maintenance of the standard orientation ; where doubt might have arisen 

 the position of the anal interradius has been marked by a *.] 



Plate VIII. — The internal cast. 



Fig. 1. — Actinal surface, showing peristoniial and anal areas clearly, and the 

 subvective grooves here occupying an almost strictly radial position and 

 marked i-v from left posterior to right posterior. 



Fig. 2. — Side view, showing the curvature of the subvective grooves. The anterior 

 groove (iii) passes across the middle of the figure. The plates of the right 

 anterior interradius (between iii aud iv) are fairly distinct. 



Fig. 3. — Abactinal surface, showing in its central area a portion of the original 

 test (compare PL X, Fig. 8). The numbers i-v here correspond to those of 

 Fig. 1, and mark the radii, while the subvective groove corresponding to each 

 number is now seen to have passed through fully one-fifth of the circumference 

 away from it : e.g. the anterior groove (iii of Fig. 1) now comes into the 

 right anterior radius (iv) . Close to number ii some matrix fills the groove, 

 and on this is the impression of a columnal of some crinoid or cystid. 

 Plate IX.— The external impression of the abactinal surface. The upper figure is 

 lit from the right hand, the lower figure from the left hand. These figures, 

 with Fig. 3 of PI. VIII, give the evidence on which PI. X, Fig. 8 is based. 



Plate X. — Enlarged details. 



Fig. 1. — A wax squeeze from a portion of the impression of the abactinal 

 surface, showing accurately the relations of the plates ; x 3 diameters. 

 Compare Forbes, pi. xxiii," fig. 7. cent, small plates of the central area.. 

 />•. a frame-plate, per. plates of the perradial area. s. suture between two 

 of the latter, apparently crenulate. (jr. portion of left anterior subvective 

 groove, col. columnal lying on matrix that fills a part of this groove. 



Fig. 2.— The peristomial region of the internal cast, slightly diagrammatised, and 

 seen from right posterior interradius ; x 2 diam. st.c. a depression where 

 a semicircular ridge on the inside of the test is supposed to have supported the 

 stone-canal ; the matrix within this would thus have underlain the madre- 

 porite. oes. matrix filling the oesophagus, c.o.fr. hollow space surrounding 

 the latter and presumed to have been occupied by a circumcesophageal frame 

 of plates (modified flooring-plates). u\v. strands of matrix bridging over 

 the space just mentioned ; they seem to be serially homologous with the podial 

 or pore scars, and may represent water-vessels connecting the adoral podia 

 with a circumoral water-ring. 



Fig. 3.— Interambulacrals showing vermiculate ornament and raised, slightly 

 crenulate suture-margins. From a wax squeeze of a fragment associated with 

 the type, x #. 



Fig. 4.— Flooring-plates in the distal region of the left anterior groove, drawn 

 from a wax squeeze of the external impression, x 6 diam. 



