DAVIDSON — SCOTTISH CAEBOXIFEEOrS BEACHIOPODA 



21 



Spirijerina cristata var. odoplicata, and Sp. insculpta are the only two species 

 belonging to tliis sub-genus that have been hitherto discovered m our Scottish 

 carboniferous rocks. 



XVII. — Spiriierina CRISTATA, var. ocTOPLicATA. J. de C. Sowerby. 

 Plate xii., figs. 36-38. 



Spirifer octoplicafus, Sowerby, Min. Con., p. 120, pi. 562, figs. 2, 3, 4 : 1827. 

 Spirijerina cristata \d,x. octopilicata, Dav. Mon. Carb., p. 38, pi. vii., figs. 37-47. 



In external shape this sheU is more often transversely sub-rhomboidal, Avith 

 nearly equally convex valves, the hinge-line being either as long or rather 

 shorter than the greatest width of the shell, with acute or rounded cardinal 

 angles ; the area is triangular, slightly concave, and of variable width. In the 

 dorsal valve the mesial fold is usually composed of a single rib, which is often 

 flattened along the middle ; but in some rare examples there exists a rudiinen- 

 tary one on either of its slopes, so that in some instances the fold assumes to- 

 wards the front an obscurely biplicated, or triplicated appearance. In the 

 ventral valve the sinus is deep and acute, while both valves are ornamented 

 with from eight to twelve angular ribs, which are (as well as the sinus and 

 fold) closely covered with numerous small granular (spinose) asperities, wliich 

 give to the shell a rough feel and appearance. The shell-structure is also per- 

 forated by minute tubuli, of which the external orifices may be readily detected 

 by the aid of a common lens. In the interior of the ventral valve a sharp 

 mesial septum rises from the bottom of the valve, and partly divides the spiral 

 cones. The species we are at present describiag varies much in general shape, 

 as well as by the number of its ribs ; it is never a large shell, although some 

 English specimens have been found more than double the size of any Scottish 

 one that has come under my observation, none of these last having exceeded 

 some six lines in length by about seven in breadth. I am also still inclined to 

 maintain the opinion expressed in my monograph, namely that the shell under 

 description bears so close a resemblance to the Permian Sp. cristata of Schlo- 

 theim that it caimot be specifically separated, and could not hi any case claim 

 more than a varietal distinction. 



Sp. octoplicata has been found at Gare, in Lanarkshire, at two hundred and 

 thirty-nine fathoms below the " Ell coal ;" at Braidwood GiU, three hundred ; 

 at Hallcraig Bridge, three hundred ; and at Ptaes three hundi'cd and forty-one 

 fathoms. The shell has also been collected in the same county at Brockley, 

 near Lesmahago ; Auchtentibber and Calderside, High Blantyre ; Capel Rig, 

 East Kilbride ; Strathavon ; and Ilobroyston, north of Glasgow. In Pen- 

 frewshire, at Arden- and Orchard-quarries, Thornhebank ; in Stirlingshire, 

 in the Corrie Burn beds ; in Ayrshire, at Roughwood and West Broadstone, 

 Beith; Auchenskeigh, near Daby; Hallerliirst, Steveuston; Craigie, near 

 Kilmarnock; and Meadowfoot, near Drumclog. It has also been found in 

 West Lothian, as well as in the Island of Ai'ran.* 



* Sp. cristata var. octoplicata is a common shell in the lower red carboniferous sandstone of 

 Kildress ; in Ireland Sp. partita of Portlock being a synonym. 



Since the pubhcation of the first pages of my paper in the December number of the 

 " Geologist," Mr. Kelly has informed me tha^t the quotation at p. 465 relative to the arrange- 

 ment of the Carboniferous system in Ireland does not represent his views, and he has Mndly 

 furnished me with the foUowing note. 



" My subdivisions are, 1, Old Eed Sandstone ; 2, calciferous-slate ; 3, limestone ; 4, coal 

 measures. The Kildress red and yellow sandstone, which is one, is not lower coal-measures ; 

 it hes" (as I have stated) "below the calciferous-slate. Again, the Old Red Sandstone is not 

 that which predominates. This rock averages about one thousand feet thick in Ireland, and 

 is not much exposed, being covered with hmestone. Our calciferous slate is considerable in 

 thickness, and in the best developed places (Clonea, near Dungarvan) is half of it made up of 

 thin bands of hmestone, the other half calcareous shale. The fossils in both inseparable, so 

 that the calciferous slate and mountain-Limestone might be considered as one division, but it 



