90 PROCEEDINGS OF THE 



the plate, apex depressed, or a little inclined downwards. Front 

 margin although arched, at right angles to the longer axis of plate; 

 anterior lateral angles rounded ; lateral and posterior margins forming 

 a continuous curve, narrowing towards the posterior end. The 

 apophyses are lateral in position, broader than long, and with a 

 rounded margin. On the under side the immediate edge of the 

 posterior margin is a little flattened. Surface marked by from one 

 to three well defined concentric grooves, which extend nearly from 

 the front margin, on one side of the keel, to that on the other ; the 

 ornamentation consists of close concentric lines of coarse papillae or 

 granules, very regularly arranged, finer on and under the apex, and 

 increasing in size towards the margins. 



Obs. — Messrs. Armstrong and Bennie have kindly lent me the 

 original plates of this species described by Messrs. Kirkby and 

 Young, but unnamed by them. Mr. Armstrong has also sent me 

 an additional example from Cunningham Baidland. The material 

 now before us is sufficient to warrant the proposal of a name for 

 this evidently distinct species. I feel, therefore, much pleasure in 

 associating with it the name of Mr. J. Armstrong, to whom I have 

 been indebted for much assistance in the study of Carboniferous 

 palaeontology. 



Chiton Armstrongianus, (Etheridge, jun.), may be recognised and 

 distinguished from other species, first by the form ; and secondly, 

 by the very coarse nature of the ornament, which resembles, more 

 than anything, the teething of a rasp, or coarse file. The outline 

 approaches nearest to that of Chiton humilis, Kirkby,* but it is 

 more pointed behind, and less acute in front ; the impressed con- 

 centric grooves less in number; whilst the portion of the plate 

 posterior to the apex is a gradual slope from the latter to the posterior 

 margin, and not nearly flat as in C. humilis, nor nearly equal to the 

 length of the remaining portion of the plate. 



Mr. Armstrong's specimen from Williamwood is a perfect one, 

 with the apophyses preserved, and three distinct impressed concentric 

 grooves. Mr. Bennie's example from the same locality is less perfect, 

 and has only one concentric groove. It is also much longer in that 

 portion of the plate between the apex and the posterior margin, in 

 this respect forming an intermediate link between C. Armstrongianus 

 proper, and C. humilis, Kirkby. 



* Geol. May , 1S67, iv\, p. 341, t. 16, f. 6 a-c. 



