112 
THE GEOLOGIST. 
where tlie spine originates. The beak is small, incnrved, and covered with a 
few slight concentric wrinkles. In the specimen nnder description the dorsal 
valve eonld not be seen, nor am I acquainted with its interior arrangement. 
The specimen here described is stated to have been derived from the north 
of Glasgow, and is preserved in the Museum of Practical Geology, in London. 
XXXI. — Productus CORA. D'Orbigny. PI. iv., fig. 13. 
Produdus cora, A. d'Orbigny, Paleontologie du Voyage dans I'Amerique 
Meridionale, p. 55, pi. v., figs. 8, 9, 10, 1842, and de Koninck, Mon. du 
Genre Productus, pi. iv., fig. 4, and pi. v., fig. 2, = Produda corrugata, 
M'Coy. 
The shells composing this species are usually longer than wide, and some- 
times irregular in their anterior prolongation ; the ventral valve is very convex, 
regularly vaulted, and at times slightly flattened along its middle ; the auricu- 
late expansions are small, but crossed by several deep undulatmg folds, which 
extend to some distance over the lateral portion of the valve, the beak being 
small and much incurved, while the hinge-line is about as long as the greatest 
widtli of the shell. The dorsal valve is concave, following closely the curves 
of the o))posite one ; both are covered with numerous longitudinal slender 
flexuous fiHform striae, wliile occasional smaller ones are implanted between the 
older, at variable distances from the beak, and which become gradually wider 
and wider, until they acquire the width of those on either side. 
Hardly any spines seem to have adorned this shell, a few only being some- 
times observable upon the aurieulate expansions, and near to the hinge-line. 
The interior has stiU to be discovered, and although the species has attained 
largish dunensions in various carboniferous districts, no Scottish example 1 
have hitherto seen did much exceed an inch in length by sometliing less in 
width. 
P. cora does not appear to have been discovered in many Scottish localities. 
In Stirlingshire it occurs in three different but consecutive stages, viz., the 
Mill Burn and Balgroehan beds, and in the Campsie main-limestone, and iron- 
stone. In Renfrewshire it may be collected at Arden quarry, near ThornUe- 
bank ; and in Ayrshire, at West Broadstone, near Beith. 
XXXII. — Productus undatus. Defrance. PL iv., fig. 15-17. 
Produdus undatus, Defr. Diet, des Sc. Nat., vol. xliii., p. 354, 1826, and De 
Koninck Monographie du Genre Productus, pi. v., fig. 3. 
In Scotland this shell does not appear to have quite attained an inch in 
diameter, is suborbieular and slightly transverse, the hinge-line being rather 
shorter than the greatest width of the shell. The ventral valve is very convex, 
with small aurieulate expansions, while the dorsal valve is moderately concave ; 
both are covered with numerous irregular, deep, concentric folds, or imdidating 
wrmkles ; and in addition the entire surface is longitudinally striated in a very 
similar manner to what we have described in the preceeding species. The 
transverse folds are very remarkable and easily distinguish the present species 
from any of the others ; they vary much, however, in their width, depth, and 
number : thus, \ipon some shells, sixteen or seventeen may be counted upon 
either valve, wliile in others they do not number much more than half as many, 
and woidd appear to have been wider and deeper in some smaller shells than m 
the larger ones. But few spines appear to have projected from the ribs. The 
interior of the valves have still to be discovered. 
P. toidatua does not appear to have been very abundant in Scotland. At 
Gare, in Lanarkshii-c, it occurs at two hundred and thirty-nine fathoms below 
the " Ell coal," and three liundi-cd and forty-tlnee at lleadsmuir. In Stirling- 
