150 



A. H. Foord — Western Australian Fossils. 



sinuated. Ventral valve flat as a rule, and very shallow, with an 

 inconspicuous horizontal and semi-truncate umbo, but in no degree 

 overhanging the hinge-line ; foramen small, circular, opening 

 upwards, but sometimes a little oblique ; sinus very faintly shown 

 on the surface of the valve, but indicated hy a forward extension of 

 the front margin. Dorsal valve moderately convex, evenly rounded 

 in outline, with little or no distinction into fold and flanks; umbonal 

 region far more marked than in the ventral valve. Surface of both 

 valves with coarse, concentric, roughened laminae. A 



"A very peculiar form of Athyris, from the persistent shallowness 



of the united valves, especially of the ventral In one or two 



places the appearance of the concentric surface lamina? would lead to 

 the belief that they projected as separate spines, after the manner of 

 Athyris Eoyssii, Lev." 



Nearly all the specimens in the Collection, with the exception of 

 the one figured on Plate VII., are crushed, but it is plain that the 

 valves were naturally much compressed, and none of them indicate, 

 so far as one can judge, the amount of convexity of the dorsal valve 

 of the specimen figured by Mr. Etheridge (loc. cit. figs. 3, 4). His 

 description of this species agrees, however, so nearly with the 

 specimens from the Gascoyne Kiver, that I have scarcely any hesita- 

 tion in referring them to it. I am fortunately enabled to give a 

 figure of the interior of the ventral valve of the present species, 

 which I have drawn on the wood, having succeeded in removing 



Athyris Macleayana, E. Eth., jun., Carboniferous, Gascoyne Eiver. 

 the matrix from one of the specimens. This supplements my 

 brother's figure (PI. VII. Fig. 3). Two other specimens show the 

 interior of the same valve, and the matrix being somewhat friable, 

 is easily cleaned out. The interior structures being thus readily 

 laid bare will afford future collectors a valuable character for the 

 recognition of the species. Only one of the specimens is sufficiently 

 well preserved to show in some places the spines which ornamented 

 the surface of the shell ; in all the others these have been rubbed 

 off, and no indication of them remains but a few faint longitudinal 

 lines, such as are seen in Plate VII. Pig. 3, which is the exter- 

 nal view of the same individual represented in the accompanying 

 woodcut (C). In this it will be seen that the dental plates are 

 united to the outer wall of the shell by a thick shelly callosity. 

 The hinge-teeth (t, t) are strong and prominent, and apparently 



