278 APPENDIX TO THE 



on either side of the upper part of the central ridge are situated large, wide, ramified 

 impressions, due to the adductor muscle, while outside and in front of these are the two 

 so-termed reniform impressions, 1 and a little under the adductor scars above mentioned 

 may be noticed a small, conical eminence (z), which will also be seen in the interior of the 

 same valve of P. giganteus. 



This is the first notice that has been given of the interior of the dorsal valve of this 

 remarkable species, and which corresponds so exactly with what we find in similar valves 

 of other Produda that no further comments upon its generic claims appear to be 

 necessary. While in ignorance of the interior character of the dorsal valve, I had, along 

 with other palaeontologists, been led to place this shell in the sub-genus Chonetes, having 

 attributed undue importance to the area and teeth, which had until then been considered 

 peculiar to Chonetes, and not to Productus ; but since the discovery of a well-defined area 

 in P. sinuatus, as well as occasional hinge-areas in P semireticulatus, P. punctatus, &c, 

 we cannot claim the area as a permanent distinguishing feature between Productus and 

 Chonetes. Mr. D. C. Davies states in his paper already referred to that P. Llangollen*) :< 

 exists in great plenty in the lower beds of the Carboniferous series at the base of the cliffs 

 near Llangollen, and that it is also found, though not so abundantly, at about the same 

 level at Llanymynech and Porthywaen; that in the Eglwseg cliffs it lies in a shale bed, 

 from which beautiful specimens of the interior of the ventral valve may be obtained. It 

 is, however, important to notice that the generality of specimens are so imperfect round the 

 margin as to lead one to imagine that they had been drifted from some distance to the 

 spot where they are at present found. 



Chonetes concentricus, Be Kon. Plate LV, fig. 13. 



Chonetes concentuica, Be KonincJc. Monograpliie du genre Chonetes, p. 186, pi. xx, 



fig. 19, 1847. 



Shell marginally semicircular, about twice as wide as long, flat in the casts ; hinge-line 

 straight, angle rounded. External surface covered with numerous sub-regular, concentric 

 ridges (thirty-seven being present on a specimen one inch and a quarter in length). 

 The largest specimen at present known measures 1^- inch in length by 3 inches in 

 width. 



Obs. In the Carboniferous Limestone at Clatteringwell Quarry, Bishop's Hill, Kenness 

 Wood, Kinross, in Scotland, were recently found a number of external and imperfect 

 internal impressions of a shell which neither Mr. Salter nor myself were at the time able 

 to determine. Upon showing the specimen here described, and belonging to the Geolo- 



1 Prof. Suess advocates the opinion that the reniform impressions are equivalent to the sunken oral 

 processes of Thecidium (?). 



