NATURAL HISTORY SOCIETY OF GLASGOW. 91 



The specimen from Cunningham Baidland is a good deal worn, 

 and is more rounded at the posterior end than the type ; it has only 

 one concentric groove. The size of the ornamenting granules and 

 their arrangement point in the direction of the Chiton plate found 

 by Mr. James Thomson, at Strathavon, (noticed hereafter). More- 

 over, looking at the size and general habit of the two plates, it is 

 a question whether it would not be advantageous to unite them 

 under one name. 



C. Armstrongianus need in no way be mistaken for the posterior 

 plate of C. Dalriensis. It lacks the short form, and two posterior 

 diagonal ridges of the latter, irrespective of other points of difference. 

 Similarly another coarsely granular species, C. gemmatus, de Koninck, 

 is at first sight seen to be also quite distinct. 



Locality and Horizon. — Williamwood, near Glasgow; in shales of 

 the Orchard limestone, Upper Carboniferous Limestone group. 



Collections. — J. Armstrong and J. Bennie. 



Collection. — J. Armstrong. Cunningham Baidland, near Dairy; 

 shales of Lower Carboniferous Limestone group, 



Chiton, sp. ind. — (Plate I., figs. 16 and 17.) 



[Compare Chiton gemmatus, de Koninck, Descrip. cles Animaux 

 Foss. Ten: Carb. Belgique, p. 323 t., 23 f., 2 c] 

 Obs. — A single intermediate plate of a moderately large Chiton 

 was found by Mr. James Thomson, in the Carboniferous beds of 

 the neighbourhood of Strathavon, and has been generally referred 

 to Chiton gemmatus, de Kon. I am under obligations to Mr. 

 Thomson for the loan of this valuable example, and beg to offer 

 the following remarks on it : — 



The surface ornament is arranged like that of Chiton gemmatus, 

 and at first sight the outline is similar. On a close comparison, 

 however, it is evident that the lateral margins in the Scotch form 

 are much more evenly rounded, and without any obliquity. More- 

 over, in the latter there existed a central obtuse keel, more apparent 

 towards the front or anterior margin. There is, also, an entire 

 absence of the faint tripartite division of the surface visible in 

 de Koninck's species. Finally, the apophyses arc much narrower, 

 longer, and project more from the front in the Strathavon specimen, 

 whilst the anterior margin is a little more concave. 



With the plate provisionally referred to Chiton Loftusianus, it 

 need not be compared, but with our C. Dalriensis there is a close 



