88 PROCEEDINGS OF THE 



is similar, and similarly distributed over the plates, only in Fig. 2 it 

 is of a more open and less crowded nature. After all, perhaps, they 

 do not differ more than. do those of some recent Chitons, so, in the 

 meantime this determination must suffice. 



These plates more closely resemble the intermediate ones of G. 

 Loftusianus, than do the anterior or posterior those of the same 

 species. Those from which PL L, figs. 2 and 4 are taken are more 

 regularly, and not so obliquely transverse as in the latter species, 

 and the lateral angles are much more rounded. The originals of 

 PL L, figs. 7 and 8 are much more sinuate than the intermediate 

 plates of the Permian species, with similar rounded, angles to 

 PL I., figs. 2 and 4. 



The Permian and Carboniferous forms are doubtless very closely 

 allied, so far as the intermediate plates are concerned, and bearing 

 this in mind I forwarded specimens to Mr. Kirkby, who replied 

 that the Carboniferous plates are smaller than most examples of C. 

 Loftiisianus, and have the lateral areas less pronounced ; he further 

 thought it would save difficulties by regarding the plates from Law 

 Quarry as undescribed. Accepting the opinion of one who has 

 worked so extensively at fossil Chitons, I beg to propose for these 

 plates the name of Chiton Dalriensis. 



There is, again, some resemblance between the posterior plate of 

 one species and that of an un-named Chiton, figured by Messrs. 

 Kirkby and Young,* but the latter is not high enough, the dorsal 

 carina is too long, and the apophyses much too near the antero-lateral 

 margin. 



PL I., figs, f 3 and 14 represent a form of posterior plate, rather 

 rare in the present collection, and which may perhaps be only a 

 variety of that just described. It possesses the general characters 

 of the latter, but the keel is continued further posteriorly, so that 

 the immediate end of the plate, instead of forming a gentle declivity 

 downwards to the margin, is abrupt and straight, or even at times 

 a little concave. From the very marked apical point thus formed, 

 there proceeds forwards a groove on each side, giving to the flanks 

 of the plate a rather hollow appearance. Generally speaking the 

 plate represented in PL I., lig. 14 has a higher appearance, and is at 

 the same time longer than the corresponding plate of C. Dalriensis 

 proper. Internally corresponding differences are perceptible. 



* Geol. Mag., 1867, iv., t. 16, f. 7, a & b. 



