DAVIDSON — SCOTTISH CAEBONITEROrS BRACHIOPODA 



99 



geologist or not, will quit the latter vallev withont visiting the 

 castle-city of Caerphilly, with its leaning tower, the most stn- 

 pendotis min in Sonth Wales, which we are told contained within 

 its walls, at the time of the memorable siege in the reign of 

 Edward II., " two thousand fat oxem twelve thousand cows, twenty- 

 five thousand calves, thirty- thousand sheep," as food for the 

 garrison. 



THE CARBOXIFEROrS SYSTEM IX SCOTLAXD CHARAC- 

 TERIZED BY ITS BRACHIOPODA. 



By THOiL\s Davidson, Esq.. F.R.S., F.G.S., Hon. Member of 

 the Geological Society of Glasgow, etc., etc. 



( Continued from Vot. Hi., p. 25. J 



TaMILT STR0PH03dINrD^. 



This family, which has been termed Orfhid^e by some authors, comprises 

 several genera and subgenera, of wliick Strophomena, Streptorhj/nchus, and 

 Orthis alone have been found represented in Scottish Carboniferous strata. 



Gents Orthis. Dahuan. 1S27. 



The genus Orthis forms a well characterized group, especially specifically 

 numerous and abundant in the Silurian and Devonian systems, is considerably 

 reduced during the Carboniferous period to appear no longer [:') in subsequent 

 stages. Two species alone have been hitherto discovered ia the Carboniferous 

 rocis of Scotland. 



XXH. — Orthis resupinata. Martin. PI. i., fig. 11-15. 



Conchi/UoUfhus anomifes resiipinatus. Martin, Petrif. Derb., pi. xlix. figs. 13- 

 14, 1S09. Terehratula resupinata, Sowerby MiiL Con., tab. 325. 



In shape it is either transversely oval, or eUiptical, but varying greatly in 

 the convexity of its valves; some examples are moderately convex, others gib- 

 bous, hence the specific denominations oi resupi?iafa, connirens, gibber a, 

 which have been appHed to what we must look upon as variations of a single 

 species. The hinge-line is straight and shorter than the greatest width of the 

 shell, with rouncfed cardinal angles ; each valve possesses a small area, of 

 which the ventral one is the largest, and divided in its middle by an open 

 trianguLar fissure. The dorsal valve is always the deepest, and either regularly 

 and evenly convex or shghtly fliittened from the middle to the front. The 

 ventral valve is shghtly or moderately convex at the rostral porrion, but be- 

 comes flattened, or even, sometimes shghtly concave as it approaches the sides 

 or frontal margia. The beak is small, shghtly prominent and incurved. Ex- 

 teriorly the suiface is closely covered with fine thread-like rounded radiating 



