DAVIDSON — SCOTTISH CARDONIFEBOUS BRACIIIOPODA. 
101 
XXIII.— OuTHis MicuELiNi* L'Evcill^. Plate i., figs. 7-10. 
Terehratula Michelini, L'Eveille, Mem. dc la Soc. Geol. dc France, vol. ii., p. 
39, pi. ii, figs. 14-17, 1835. = Sinrifera fdiaria, Phillips' Gcol. of York., vol. 
ii., p. 220, pi. xi, fig. 3, 183G. 
Tliis .Orthis is cither circular or longitudinally subtrigonal, the greatest 
width bcmg situated in the frontal half, while the front itself forms cither a 
gentle outward, or a sUght inward curve. The Mnge-line is abbreviated, and 
at times does not attain one third the width of the shell ; both areas are con- 
sequently very small ; but that of the ventral valve is the largest, and divided 
by an open triangidar fissure. The dorsal valve is moderately convex, with a 
gentle depression towards the front, while the ventral one is very shallow, 
slightly convex at the beak and along the' middle, from whence it becomes much 
flattened towards the margins. The depressions of the ventral valve and slight 
convexity of the dorsal one give to the shell a general depressed appearance, 
which is one of the features by which it can be distinguished from 0. resupi- 
nata. The beak of the ventral valve is small, slightly incurved, and projecting 
but little beyond the level of that of the dorsal valve. The surface of the shell 
is ornamented by numerous small radiating tlircad-like rounded striae, which 
rapidly increase in number by numerous intercalations, while from all these 
little ribs numerous small hair-like hollow spines project, becoming more 
closely packed towards the margins, so that, when alive, the whole shell must 
have been invested with delicate spines, no where exceeding a quarter of an 
inch in length. Prof, de Koninek who, in 1813, first noticed the spiny in- 
vestment, was of opinion that the dorsal valve was alone so provided, but I can 
assure my distinguished friend that, although in the generality of specimens 
the spines on the dorsal valve were the most numerous, I possess several ex- 
amples which prove beyond doubt that the ventral valve was also so provided, 
although generally not to the extent seen on the dorsal one. In addition to 
the spines, the whole siu'face of the shell is covered with minute punctiires, 
wliich are the external orifices of the tubuli or perforations which traverse the 
entire thickness of the valve. It will not be necessary to describe in detail 
the markings observable upon the interior surface of the valves, as I have 
done so for 0. resupvmta, but a glance at the respective illustrations will suf- 
fice to explain the diiferenees in the species under description. These in the 
ventral valve are evinced in the narrowness of the median ridge and less in- 
clined slope of the occlusor muscular impressions ; while in the dorsal valve 
the space occupied by the occlusor, devaricator, and ventral adjuster muscles 
is wider than in 0. resupinata ; there is also a singular impression at the base 
of the fissure marked N. in the figure, and which is with some uncertainty 
referred to the pedicle muscle. 
0. Michelini is not a rare shell in Scotland. In Lanarkshire it occurs at 
Laugshaw Burn at three hundred and seventy -five fathoms lower than the 
" Ell Coal ;" at Broekley and Middleholm, near Lesmahago ; Auehentibber, 
Calderside, and PhiUipshill, High Blantyre ; Capel Big, East Kilbride ; and at 
Robroyston, north of Glasgow. In Reiifrewshii-e, at Orchard-quarry, ThornHe- 
bank ; Barrhead and Howood, near Paisley. In Ayrshire, at Roughwood, 
West Broadstone, and Treehom, near Beith; Auchenskeigh, Dahy, Gold- 
craig, and Monkredding, near Kilwinning ; Hallerhirst, Stevenston ; Craigie, 
near Kilmarnock, and Cessuoek near Galston. In Stirlingshire it is found in 
several stages. At Craigenglen, the Campsie main-limestone and Corrie Bum. 
In Dumbartonshire, at Castlecary. In Eifeshire, at Charlestowu and Limekilns, 
above Queensferry. 
* Anomias ttriata of Ure, "History of Rutherglen and East Kilbride:" 1793. PI. xiv., 
figs. 13 and 14. ^ 
