DAVIDSON — SCOTTISH CARBONIFEROUS BEACHIOPODA. 



475 



being more often divided into tiiree or four lobes from tlie central fold, present- 

 ing a narrow mesial groove, while a longitudinal and somewhat angular sinus 

 extends from the extremity of the beak to the frontal margin in the dorsal one. 

 The beak is not much produced or incurved, and is truncated by a small cir- 

 cular foramen, which lies contiguous to the umbone of the smaller valve. 

 Externally the shell is smooth, being marked only by a few lines of growth. 

 In the interior the spiral appendages are directed outwards, as may be seen in 

 the figure, lign. 3. page 99, of this volume. 



In the larger, or ventral valve, the hinge-teeth are supported by vertical 

 shelly plates, and the free space at the bottom of the valve between and beyond 

 these is filled up with muscular impressions. The muscle, whose function was 

 the closmg of the shell, has formed a small elongated, mesial, heart-shaped 

 scar ; and under, as well as along the outer side, are seen the impressions of 

 the cardinal or divaricator muscles — that is to say, of those which had the 

 ofi&ce of opening the shell, the impressions of the pedicle, or ventral adjustor 

 muscle may also be detected, on either side, close to the adductor. In the in- 

 terior of the smaller or dorsal valve the hinge-plate presents four depressions, 

 which afforded attachment to the dorsal pedicle, or dorsal adjustor muscles ; 

 the hinge-plate is likewise perforated close to its summit (under the umbone) 

 by a minute circular aperture. On the bottom of the valve, divided by a small 

 longitudinal ridge, may be seen the quadruple impressions left by the adduc- 

 tor, or posterior and anterior occlusor muscles. These details are beautifully 

 displayed in some valves from Capel Rig, East Kilbride, which were kindly 

 communicated by Mr. Armstrong, and which wiU be found represented in 

 pi. xii., figs. 8-9. 



Some specimens of this shell from Lanarkshire (wherein the mesial groove 

 of the dorsal valve was not so apparent or distinctly marked as in the ordinary 

 and typical shapes of the species) have been referred by Professor M'Coy to 

 Phillips' A. globularis, but of which species I have not hitherto seen any well- 

 authenticated Scottish examples. Some specimens have likewise presented 

 externally a deceptive appearance of striation, but which is not the character 

 of the well -preserved shell. 



Athyris amUgua is one of the commonest of the Scottish carboniferous 

 species. In the parish of Carluke it is plentiful in the upper limestone series, 

 but also hundreds of fathoms lower in the series — that is, in the sheUy lime- 

 stone band, a few feet above the "Productus giganteus bed."* Thus at Gare it 

 may be collected at two hundred and thirty-nine fathoms, at Braidwood Gill at 

 three hundred and ninety-three fathoms, and at Langshaw at three hundred and 

 forty-three fathoms below the horizon of the "EU coal." In Lanarkshire (besides 

 the localities just mentioned) it is found at LaAvrieston and Capel Rig, East 

 Kilbride ; at Calderside and Auchentibber, High Blantyre ; at Brockley, near 

 Lesmahago ; and Robroyston to the north of Glasgow. In Stirlingshire it is 

 found at Campsie, in the Craigenglen, Balglass, MiU Burn, Balgrochen, Main 

 limestone, and Corrie Burn beds. In Renfrewshire it. is plentiful at Eloor's 

 quarry Johnstone Bridge, Barrhead, Arden quarry, and Orchard, near Thorn- 

 liebank. In Ayrshire it occurs at Roughwood and West Broadstone, Beith ; 

 at Auchenskeigh, Daky ; Goldcraig, Kilwinning, Hallerhirst, Stevenston ; and 

 Craigie, near Kilmarnock, &c., &c. It is also found in the Island of Arran. 

 In Haddingtonshire it is to be collected at Cat Craig, near Dunbar ; and in 

 many other places which need not be enumerated. 



* In Ireland it is most abundant, under the shape of casts in the red sandstone of 

 Kildress which is still lower down in the series than is the great "Productus bed" above 

 referred to. 



