Kirkhy and Young — On Fossil Chitons. 341 



Another plate of the same kind occurs among Mr. Burrow's recent discoveries, and we 

 venture to identifj"^ both it and the former one with the last-named species . 



4. CMton (?) cordatus, Kirkby, 1859. [Quart. Journ. Geol. Soc, 

 vol. XV. p. 616. pi. xvi., figs. 24, 27, 54.] Plate XTL. Figs. 10a, h, 

 11a, b. 



An intermediate plate, and, I helieve, an anterior one, occur among the Yorkshire 

 specimens. Both are larger than the Permian specimens from which the species was 

 described. 



The intermediate plate is almost cordate in shape, being comparatively broad, 

 rounded, and centrally sinuated anteriorly, and extremely narrow and acuminate 

 posteriorly, — the anterior, lateral, and posterior margins blending insensibly together. 

 The median line is slightly arched ; the lateral areas occupy less than two-thirds of the 

 plate -surface, and are separated from the dorsal area by a slight sulcus. The surface 

 is finely granulated ; length, half an inch, and the same in breadth. 



The anterior plate is semi -cone shaped ; is over half an inch wide, three-eighths of an 

 inch high, and a quarter of an inch long. It is thick-shelled, and has the surface 

 covered with rather coarse, oval granulations, regularly arranged in concentric lines. 



Both these plates closely resemble the type specimens of C. cordatus, except in the 

 granulated surface of the anterior plate, which differs both from the intermediate plate 

 we describe here and from the Permian specimens. It may possibly belong to another 

 species, but as it comes so close to G. cordatus in other characters, we place it along 

 with that species for the time being. 



5. Chitonellus (?) suhantiquus, sp. nov. Plate XVI. Figs. 12a, b, 13. 

 We describe two patelliform plates under this genus, as we consider them to be 



plates of Chitonellus, though as the marginal processes of insertion are not exposed, 

 our opinion as to their generic position can scarcely be free from doubt. They evi- 

 dently belong either to that genus or to one of the groups of Patelliform Gasteropoda, 

 though we believe to the former. Indeed, one plate so nearly approaches the Permian 

 species C. antiquus, Howse (see fig. 17, pi. xvi. Quart. Journ. Geol. Soc), as to render 

 its separation from it a matter of difficulty. The following is a brief description of 

 the most perfect plate, which we take to be an intermediate one. 



Conical, sub-pentagonal in marginal outline, apex recurved and placed rather be- 

 hind the centre of the plate. Several fine ribs radiate from the apex down each side, 

 and others appear to have originally existed in front and behind, but are not now 

 visible on this specimen, owing to the imperfect preservation of the shell in these 

 parts. Surface marked with strong lines of growth; length rather under three- 

 eighths of an inch ; breadth rather over two-eighths of an inch. 

 Description of Scotch Specimens : — 



1. Chiton humilis, Kirkby, 1865. [Trans. Geol. Soc, Glasgow, 

 vol. ii. p. 14, pi. i., fig. 1.] Plate XVI. Figs. 6a, b, c. 



This species was discovered two years ago and described in the Transactions of the 

 Geological Society of Glasgow. The only perfect plate found is a posterior one, which 

 we re-figure. It occurs in calcareous shale in the Kobroystone beds N.E. of Glasgow. 



2. Chiton sp. Plate XVI. Figs. 7a, b, c, 9. 



Mr. Jas. Armstrong and Mr. Jas. Bennie, of Glasgow, have found three posterior 

 plates in the Carboniferous Limestone Shale of Williamwood, near Cathcart, in Ren- 

 frewshire, which differs from the preceding species. They are relatively broader, 

 more pointed in front, and more sharply angulate, and with coarser surface granula- 

 tions than the equivalent plate of C. humilis. They are about one-fifth of an inch wide, 

 and the same or a little less in breadth, and show well-developed processes of in- 

 sertion. 



These plates approach nearest to Chiton Burrowianus of any Chiton known to us ; 

 but they do not come near enough to allow them to be identified with that species. We 

 leave them for the present unnamed. 



3. Chitonellus Youngianus, Kirkby, 1865. [Trans. Geol. Soc.. 

 Glasgow, vol. ii. p. 14, pi. i., fig. 2.] Plate XVI. Figs. 2, 3, 4. 



Since the discovery of a single plate of this species in 1865, portions of two others 

 have been_.found. These we figure along with the first. 



