112 



THE GEOLOGIST. 



where the spine originates. The beak is small, incurved, and covered with a 

 few slight concentric wrinkles. In the specimen under description the dorsal 

 valve codd 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.— PnoDUCTUs CORA. D'Orbiguj. PL iv., fig. 13. 



Produdus cora, A. d'Orbigny, Paleontologie du Yoyage 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, = Producta 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 undulating 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 

 width of the shell. The dorsal valve is concave, following closely the curves 

 of the opposite one; both are covered with numerous longitudinal slender 

 fiexuous filiform striae, while occasional smaller ones are implanted between the 

 older, at variable distances from the beak, and which become gradually wider 

 and ^\^der, until they acquire the width of those on either side. 



Hardly any spmes seem to have adorned this shell, a few only being some- 

 times observable upon the auriculate expansions, and near to the hinge-line. 

 The interior has still to be discovered, and although the species has attained 

 largish dimensions in various carboniferous districts, no Scottish example I 

 have hitherto seen did much exceed an inch in length by something 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 Balgrochan beds, and in the Campsie main-limestone, and iron- 

 stone. In Kenfrewsliire it may be collected at Arden quarry, near Thornhe- 

 bank ; and in Ayrshire, at West Broadstone, near Beith. 



XXXII.— Peodijctus undatus. Defrance. PI. iv., fig. 15-17. 



Productus nndatus, Defr. Diet, des Sc. Nat., vol. xliii., p. 354, 1826, and De 

 Koninck IMonographie du Genre Productus, pi. v., fig. 3. 

 In Scotland this sh(;ll docs not appear to have quite attained an inch in 

 diameter, is suborbicular and slightly transverse, the hinge-line being rather 

 shorter tlian the greatest width of the shell. The ventral valve is very convex, 

 wit h small auriculale expansions, while the dorsal valve is moderately concave ; 

 l)otli arc covered with numerous irregular, deep, concentric folds, or undulating 

 wi-iiikles; and in addition the entire surface is longitudmaUy striated in a very 

 similar manner to what we have described in the preceeding species. The 

 t rausvcTse folds arc very ren\arkal)le and easily distinguish the present species 

 from any of the others ;' they vary iinich, however, in their width, depth, and 

 number: tlnis, upon some shells, sixteen or seventeen maybe counted upon 

 either valve, whil<^ in others they do not number nuieh more than half as many, 

 aud would appear to have been wider and deeper in some smaller shells than in 

 the larger ones. But few sjunes appear to have projected from the ribs. The 

 interii)r of the valves have still to be discovered. 



P. tfudtrfus does not appear to have been very abundant in Scotland. At 

 (lare. in Lauarkshire. it occurs at two hundred aiid thirtv-nme fathoms below 

 the " Kll eoal." aud three hundred and forty-three at lleadsmuir. In Stii'ling- 



