THK GEOT.OGrST. 
Sp. pi>/ff///s, S/i. ort/lis, Sp. f/l(iliiYi, Sp. Cnrliili-i.piisis, Sp. Urli, and Sp. Uncala ; 
and it nuist also be further noted that some of these have hilhcn to ])roved 
exceedingly rare, and that good exain])les of several others arc with dillicidty 
obtained. 
VIII. — Spirifeka nuPLicicosTA. Phillips. PI. xii.,* figs. 14, 15. 
Spirifera dupUcirostfi, Phillips, Geol. York., vol. ii., p. 218., pi. x., fig. 1, 1836; 
and Uav. Garb. Mon., p. 21, pi. iii., ligs. 7^10, pi. iv., Iigs. 3, 5— ll.f 
This shell varies much in external shape, being cither transversely sub-rhoni- 
boidal or somewhat longer than wide. The valves arc moderately convex, with 
a more or less elevated mesial fold in the dorsal, and a corresponding sinus in 
the ventral one. The hinge-line is shorter tliau tlic width of the shell, the area 
of moderate breadth, and the beak more or less incurved. The valves arc onia- 
niented by numerous radiating ribs, wliicli augment in number at various dis- 
tances from the beaks by intercalation and bifurcation. The ribs vary, how- 
ever, somewhat in general a])pearauce in difl'erent specimens, being only here 
and there dupUeose, or having three or four ribs clustered together; the term 
duplicicoda is, therefore, very inajipropriate, since many species of the genus 
present the same peculiarity. 8p. diiplicicosta is the largest Scottish spulfcr 
with wliich I aui at present acquainted, some specimens measuring twenty-one 
lines in length by about thu'ty in width ; and it has also been sometimes eon- 
founded with Sp- striata of Martin — a closely allied species, but of which I am 
not acquainted with any well authenticated Scottish example. 
Perfect specimens of this shell are rarely found, althoun-li thousands of 
crushed or oroken valves occur in a bed of linu^stonc, four leet in thickness, 
near Campsie, at Balgrochan, and Corrie Burn, in Stirlingshire. In Ayrsliirc it 
is found at West Broadstone, near Bcith ; at Craigie, near Kilmarnock ; and at 
Auchenskcigh, near Dairy. In Lanarkslm-e it has been collected at Brocklcy, 
near Lesmahago. It has been also found in West Lothian and Bute. 
IX. — Spirifera bisulcata. Sowerby. PI. xii., figs. 19 — 25. 
Spirifera bisidcatm, J. de C. Sow., Min. Con. Tab., 492, figs. I, 2, 1825 ; 
Spirifera bisulcata, Dav. Mon. Carb., p. 31, pi. iv., fig. 1, pi. v., fig. 1, pi. vi., 
figs. 1 — 19, and pi. vii., fig. 4. 
This shell is cither transversely semi-circular or obscurely sub-rhomboidal, 
the valves being almost ccjually deep or convex. The hinge-line is sometimes 
rather shorter than the greatest \vidth of the shell, with the cardinal angles 
rounded ; or as long, with angles of variable projection. The area is sub- 
parallel, of moderate width, and divided by a triangular fissure, the beaks 
incurved, and at times very approximate. In the dorsal valve the fold is somc- 
wliat angidar, and of greater or lesser elevation, but is at times so flattened 
that it hardly rises above the general convexity of the valve. The sinus is of 
moderate depth. Each valve is ornamented with from tliirty to fifty obscurely- 
rounded ribs, which increase in number by the occasional iDifurcatiou or inter- 
calation of smaller ribs at various distances from the beaks. On the mesial 
fold they are arranged into three groups, separated by sulci of greater depth, 
the whole surface being also regularly covered with imbricating stria;. 
The variations in shape presented by this species are quite perplexing, and 
it is probable that several so termed species will require to be added to its 
synonyms. Among these we may mention Sp. seiidcircttlaris, Phillips, and Sp. 
crussa, dc Kouiuck, ccrtaiidy ; and possibly Sp. (jrandirmtuta of M'Coy. 
* Tliis plate forms part of the second voliirao of the "Geologist." 
t For list of s.^nioiij-ms, &c., sec my monoffi'aph published by the PaliEontOfjraphical 
Socioty, all details not absolutely rerjuired having been omitted in the present monograph. 
