DAVIDSON — SCOTTISH CAIiliONIFEROUS nRACHIOI'ODA. 
475 
l)oins more often divided into tiu'ce or four lobes from the central fold, present- 
ing a narrow mesial groove, while a longitudinal and somewhat angular sinus 
extends from t he extremity of the beak to t he frontal margin in the dorsal one. 
The beak is not nnieii i)roc\ueed or incurved, and is truncated by a small cir- 
cular foramen, which lies contiguous to the nmbonc of the smaller valve. 
Externally the shell is smooth, being marked oidy by a few lines of growth. 
In tiie interior the spiral appendages are directed outwards, as may be seen iii 
the tigurc, lign. 3. ])age 'J'J, of this volume. 
In th(! larger, or ventral valve, the hinge-teeth arc supported by vei'tical 
shelly plates, and t he free space at the bottom of the valve between and beyond 
these is tilled up with muscular impressions. The muscle, whose function was 
the closing 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 cardiuiJ or divarieator muscles — that is to say, of those which had the 
oflicc of opening the shell, the hnpressions 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 liinge-plate presents four depressions, 
which afforded attachment to the dorsal pedicle, or dorsal adjustor muscles ; 
the liinge-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 quacbuple impressions left by the adduc- 
tor, or posterior and anterior oeelusor muscles. These details are beautil'ully 
dis])layed 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. S-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. glohulariH, but of which species I have not hitherto seen any weU- 
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. 
Aflijjris amhigwa 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 shelly lime- 
stone band, a few feet above the "Produetus giganteus bed."* Thus at Gare it 
may be collected at two hundred and thirty-nine fathoms, at Braidwood GiU 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 Lanarkshu-e (besides 
the localities just mentioned) it is found at Lawrieston and Capel Rig, East 
Kilbride ; at Calderside and Auehentibber, High Blantyre ; at Brockley, near 
Lesmahago ; and Robroyston to the north of Glasgow. In Stii-lingshire it is 
found at Canipsie, in the Craigenglen, Balglass, Mul Burn, Balgroehen, Main 
limestone, and Corrie Burn beds. In Renfrewshire it is plentiful at Floor's 
cjuarry Johnstone Bridge, Barrhead, Arden quarry, and Orchard, near Thom- 
liebaiik. In Ayrshire it occurs at Roughwood and West Broadstone, Beith ; 
at Auehenskeigh, Daky ; Goldcraig, Kilwinning, HaUerhirst, Stevenston ; and 
Craigie, near Kilmarnock, &c., &c. It is also found in the Island of Arran. 
In Iladdingtonshire 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 
Kildi-ess which is stiU lower dovm in the series than is the great "Produetus bed" above 
referred to. 
