JURASSIC AND TRIASSIC BRACHIOPODA. 191 



d'Orb., from the Upper Neocomian rocks of the south of France. It varies likewise very 

 much in the number and strength of its ribs ; but this is a feature common to every 

 species of the genus. 



This shell appears to be a common fossil in the Upper Oolitic Grey Limestone (sub- 

 coralline beds ?) at Garty, in Sutherland. 1 



The specimens figured having been communicated by the Rev. J. M. Joass from the 

 Dunrobin Museum, I have named the species after his Grace the Duke of Sutherland, in 

 humble appreciation of the services he is rendering to science by the formation of a local 

 Museum at Dunrobin, in Scotland. 



180. Rhynchonella inconstans, Sow. Dav., Ool. Mon., p. 87, PL XVIII, figs. 1—4 ; 



and Sup., PI. XXVI, figs. 1—6. 



I have not much to add to the description I gave of this important species at p. 87 of 

 my Oolitic Monograph. I have always considered that in dealing with a species, or in 

 comparing it with others, full-grown examples should be made use of, for the animal has 

 then acquired all its characters. Variations in shape, due to age, should be afterwards 

 considered. This is especially necessary with Bh. inconstans, for when full grown it 

 attains to fully 1 inch 8 lines in length, by 1 inch 9 lines in width, and 1 inch 3 lines in 

 depth, being very globose and gibbous. The fold and sinus, being but slightly defined or 

 raised above the general convexity of the shell, are shifted either to the one or other half of 

 the shell, thus giving it a twisted or contorted and unsymmetrical appearance. The 

 surface of both valves is also, in the full-grown form, marked with from thirty to forty 

 simple, regular, radiating ribs or costae, scarcely ever exceeding two lines in breadth (if 

 as much) and one in height. I have seen many specimens agreeing with the typical 

 form above described, from the size of less than two thirds of an inch to the dimensions 

 of the full-grown individuals above noticed (see ' Ool. Mon.,' PI. XVIII, figs. 1 — 2; and 

 Sup, PI. XXVI, figs. 1, 2). 



We will now notice the exceptional shapes assumed by this most variable species, and 

 the one that can be sometimes almost confounded with a closely allied form occurring in 

 the Supra-coralline red rock of Abbotsbury. In Sup., PI. XXVI, figs. 3 — 6, will be 

 seen examples of this variety from the Kimmeridge Clay of Wooton Basset, and Shotover 

 Hill, near Oxford. Fig. 3 shows a symmetrical shell, much resembling in size and shape 

 some specimens of Bh. obsoleta. In this form the mesial fold is in the middle, a very 

 uncommon occurrence in Bh. inconstans. In fig. 4, from the same locality, we have the 



1 For a full description of this important locality, as well as that of Allt-na-cuil, see Prof. Judd's 

 admirable memoir "On the Secondary Rocks of Scotland," 'Quart. Journ. of the Geol. Soc.,' vol. xxix, 

 p. J 79 and 182, 1873. 



