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BRITISH DEVONIAN BRACI1IOPODA. 



enclose the dental sockets ; under the cardinal process a convex ridge of moderate width 

 separates the quadruple impressions of the adductor or occlusor muscle, these last pro- 

 ducing two oval- shaped depressions, one placed above the other and separated by lateral 

 elevations branching from the central ridge. 



Dimensions variable; length 7, width 9, depth 4 lines. 



Obs. All the specimens I have been able to examine of this species were in the 

 condition of internal casts and external impressions, but which being sharply marked, it 

 was possible to reproduce the surface of the shell by the means of gutta-percha. By this 

 medium we have also the exact external shape as well as of the interior details of the 

 valves, in as complete a condition as if we had the shell itself before us. 



Some palaeontologists have considered, but with a mark of interrogation, 0. operculans, 

 De Verneuil, and 0. orbicularis, of the same author, as synonyms of 0. interlineata ; but 

 I have not been able, as yet, to feel quite certain with reference to these identifications. As 

 observed by Prof. M'Coy, 0. interlineata varies considerably in proportionate width, but 

 this is principally owing to pressure. It occurs abundantly in the Upper Devonian shales 

 of Landlake, near S. Petherwin, and Launceston, in Cornwall ; and in the brown grits of 

 North Devon, such as near Barnstaple, Croyde, Marwood, &c.; and, according to Mr. Valpy, 

 in the Middle Devonian at Hagginton Hill, near Ilfracombe. 



Orthis granulosa, Phillips. PI. XVII, fig. 24. 



Ouihis geakvlosa, Thil. Pal. Foss. Devon, &c, p. 65, pi. xxvi, fig. 1 11, 1841. 



Spec. Char. " Orbicular, very depressed, lenticular. The hinge-line above half the 

 width of the shell. Surface radiated, with numerous fine, granulated striae, of unequal 

 length, doubled in number and diminished in prominence towards the margin, so as to 

 give it rather a bordered appearance. Loc. In North Devon, Woodabay. In South 

 Devon, Meadsfoot Sands." {Phillips.) 



Obs. I have been able to examine only two or three incomplete valves of this species, and 

 therefore have preferred to reproduce Phillips's description, which conveys all the information 

 we at present possess. Mr. Pengelly has found in the Middle Devonian Limestone of 

 Woolborough quarry a valve (the one figured in our plate) which quite agrees with 

 Phillips's description and figures. In this specimen forty-five small ribs may be counted 

 round the margin, the valve being slightly convex and measuring five lines in length by 

 five and a half in width, and which is also about the proportion of Phillips's figure. Prom 

 such imperfect and insufficient material one can say but little as to the specific value 

 of this form, and it is to be hoped that further search may bring to light some examples 

 showing both valves, area, &c. 



