﻿Vol. 64.] CA^RBONIFEROCrS LHIESTONE OF THE MIDLAND AEEA. 79 



the shell, the pits in the radial furrows are small and closely- 

 packed. 



Dimensions. — The hinge-line of an average specimeti measures 

 about 6 centimetres. Large specimens attain a width of 8 or 

 9 centimetres. 



Horizon. — Clionetes compressa occurs in the Lonsdalia-^'xxbzoYiG 

 of the Midland area, and is apparently confined to that subzone. 

 Locally, it attains great abundance. 



Discussion. — The characters of flattened form, large size, and 

 fine ribbing, possessed by Clionetes compressa^ would generally 

 determine its reference to Ch. papilionacea (Phil.). 



Since the holotype ^ of Ch. papilionacea is an imperfect specimen, 

 exhibiting only a part of the interior of the brachial valve, with 

 small attached fragments of the marginal part of the pedicle-valve, 

 the species is actually very insufficiently known. All large, 

 flattened, finely-ribbed Carboniferous Clionetes have been, however, 

 generally referred to Ch. papilionacea (Phil.), consequent upon 

 Davidson's ^ recognition of that species. Until the nomenclature 

 of the group has been adequately revised, some such unsatisfactory 

 method is unavoidable ; and the plan of employing the term 

 ' papilionaceous Chonetes ' to connote members of the group seems 

 advisable, in that it emphasizes the unsatisfactory state of their 

 nomenclature. 



The application of a distinctive name to the form here described 

 and figured seems to me to be both justifiable and expedient. 

 Chonetes compressa is distinguished from all other papilionaceous 

 Chonetes by its remarkably-flattened form ; and it has, apparently, 

 a very limited vertical range in the Carboniferous Limestone. I 

 have compared specimens of Ch. compressa with the t3'pe-specimen 

 of Ch. papilionacea ; and, so far as the imperfect nature of the 

 latter admits of a comparison, the following differences may be 

 noted : — (1) The pedicle-valve of Ch. papilionacea is appreciably 

 convex (this is inferred from the concavity of the brachial valve in 

 the type-specimen), whereas that of Ch. compressa is almost com- 

 pletely flat. (2) Ch. papilionacea is a larger and more transverse 

 shell. (3) Spine-apertures are stronger and more numerous on the 

 ribs of Ch. compressa. 



Without contending for the specific distinctiveness of Ch. com- 

 pressa., I consider that, in a subsequent revision of the papilionaceous 

 Chonetes., it must be recognized as a well-defined type, characteristic 

 of a limited horizon, and that a distinguishing appellation is 

 therefore desirable. 



^ Now preserved in the British Museum (Natural History), South Kensington. 



■■^ See 'Monogr. Brit. Foss. Brachiop.' (Palaeont. Soc.) vol. ii(18'^8-()3) p. 182 

 & pi. xlvi, figs. 3-5 />. Davidson states that figs. 3 & 4 of liis plate represent 

 tlie original specimen. But these figures depict a wonderfully-perfect sliell, 

 and can only be regarded as an imaginative restoration. 



