94 PROCEEDINGS OF THE 



dorsal area. In the Permian variety the latter proceed forwards 

 from the apex itself, but in the Carboniferous form from a point 

 about half-way between the posterior termination of the plate and 

 its front margin. Further, G. contains has previously been noticed 

 as a Carboniferous fossil by Kirkby and Young, which will 

 strengthen the reference now made. 



Lastly, these plates have a certain resemblance to Chiton 

 mewvpiscus, de Ryckholt, but to cany out a detailed comparison 

 with this species, actual specimens are necessary. 



The terminal plate of the recent Chiton haded us Sow., much 

 resembles the plate now described. It has a similar recurved under 

 portion, but the recent form lacks the arched appearance of the 

 fossil species. 



Locality and Horizon. — Law Quarry, near Dairy, as before. 



Collections. — J. Bennie, J. Smith, &c. 



Chiton GeiJiiei, sp. nov. — (PI. II., figs. 1-3.) 



Sjp. Char. — Anterior plate semi-conical, snout-like, and convex, 

 anteriorly pointed, posteriorly truncately rounded ; lateral margins 

 straight from the pointed extremity to the posterior lateral 

 angles. The middle of the plate is a little flattened, and the sides 

 somewhat bent down. Surface crowded with blunt microscopic 

 tubercles arranged in transverse lines, with here and there growth 

 lines; lateral margins bearing a row of acute spirelets. On the 

 underside of the plate there is a recurved margin at the bluntly 

 pointed extremity, and either about the middle, or towards the 

 posterior, there is a thickened transverse ridge. 



Posterior plate square oblong ; anterior margin truncate ; pos- 

 terior margin rounded ; middle line bluntly carinate ; flanks 

 directly bent clown, not hollowed out. The dorsal ridge terminates 

 at about two-thirds from the anterior margin in an almost imper- 

 ceptible apex ; a ridge proceeds from this point downwards on each 

 side, in a slightly forward direction. The surface of the plate 

 behind this line is rounded, and curves obliquely downwards to the 

 posterior margin. Immediately behind each of the previously 

 described ridges is a corresponding groove, or sulcus. The surface 

 is highly granulated, whilst a line of sharp spinelets, similar to 

 those on the anterior plate, is placed along each diverging ridge. 

 Apophyses small, close to the antero-lateral angles. 



Obs. — The presence of the little spinelets, which assist to ornament 



