292 Proceedings of the Royal Physical Society. 



casts of the ventral valve, and compare the casts from Aus- 

 tralia with the fine interior of >S'. Golclfussi (Munster), figured 

 by Mr Davidson.* It will be observed that in Mr Davidson's 

 fig. 9, representing a cast in a similar state of preservation to 

 our specimens, there is, as in the latter, the correspondingly 

 blunt and gradually attenuated but prominent beak (figs. 29 

 and 30, i, i), and deep pits left by the teeth of the ventral 

 valve (fig. 30, a). Again, compare in fig. 10 of the " Permian 

 Monograph" the concave or grooved back of the umbo with 

 that of the Queensland cast (figs. 27-30, h). Thirdly, the 

 position of the adductor scars in the same Permian figure is 

 quite comparable with that of the Australian specimens (figs. 

 26-30, c, c, c, c), and more particularly with fig. 27. In Mr 

 Davidson's figure the deep pit or fossa in front of these im- 

 pressions is not so marked as in our fig. 29 ; but this is itself 

 a variable point in the Australian shells. It is not as deep 

 in fig. 26, and still less so in fig. 27 or 33. With regard to 

 the cardinal muscular scars, we observe a perfectly similar 

 arrangement — the position identically the same, similar ridg- 

 ing and grooving, the only apparent difference being that in 

 the Permian >S'. Goldfitssi the abrupt or scarp-like side appears 

 to be towards the front, whereas in S. Clarkei it is towards 

 the umbo or hinge-line (figs. 27 and 29, e, e, e, e). 



Having, I hope, at least shown the resemblance of the 

 sandstone casts to the genus Strophalosia, it may perhaps be 

 well to say a few words on their relation one to the other, 

 chiefly on account of the great disproportion in the develop- 

 ment of the central eminence, causing the deep pit in casts, 

 and from the less marked appearance of the muscular scars 

 and internal portions generally. I find the central eminence 

 to be a very variable character amongst these shells. We 

 have one extreme in fig. 29, and the other in fig. 33. Be- 

 tween these two there is every gradation (figs. 26, 27, 28, d, d, d) 

 in depth, and the same may be said of the muscular impres- 

 sions, although they appear to be less open to variation than 

 other parts. 



We may now pass on to a consideration of the dorsal 

 valves of S. Clarkei, and for this purpose the material we 



* Mon. Permian Bracli., Pal. Soc, t. 3, figs. 9 and 10. 



