248 NOTES ON THE PERMIAN SYSTEM OF 



by comparing his figure, Perm. Men. pi. 11, fig. 10, with Mr. 

 Davidson's Mon. Brit. Perm. Brach. pi. 4, figs. 19, 21, and with 

 good casts from Humbleton or interiors from Tunstall. The 

 most incorrect part of Mr. King's restoration is the strongly 

 granulated or obscurely dendritic appearance of the adductor 

 muscular impressions, which are also eiToneously divided into 

 two sets; and the reniform inijDressions are made to take their 

 origin in these more distinctly than is warranted by the appear- 

 ances of these parts in good specimens. The cardinal-process, 

 the hinge -margin, and the spine-like callosities on the inner 

 surface of the shell are also all very imperfectly represented. 

 The latter, indeed, are rej^resented covering the w^hole of the 

 cardinal, or, as it may be termed, the ovarian region, which, 

 instead of being studded with spinous callosities, should be 

 minutely pitted. Dr. Geinitz's figures of the same valve are 

 more correct than the one already mentioned, but the adductor 

 muscular impressions are too leaf-like and lobed. All the other 

 figures of this valve that have been published since 1850 appear 

 to be merely copies from King's. It appears rather strange that 

 the interior of the lower valve is neither figured nor described in 

 the Perm. Monograph. 



The hinge-line of the upper valve is not quite straight, but 

 slightly angulated, the angle being strongest near the cardinal- 

 process. This cardinal-process or lever varies slightly in form, 

 but is generally bifid at the extremity, each part being again slit 

 by a deep triangular groove or furrow. When in situ it fills nearly 

 the whole of the umbonal cavity of the lower valve, and rests 

 against its inner surface. It may thus assist in keeping the 

 valves in position. About the base of the cardinal-process the 

 shell is very much thickened, and from it a strongish ridge runs 

 along on each side parallel to the hinge-margin, which gives to 

 the latter a bevelled appearance. On the outer side of this ridge 

 is seen the row of de23ressions caused by the cardinal spines. 

 From the base of the cardinal-process a thin plate or septum 

 proceeds straight forwards into the cavity of the shell, becoming 

 deeper and free in front ; it separates the adductor muscular im- 

 pressions and the reniform callosities, to which latter the oral 



