18 



THE GEOLOGIST. 



wide and produced, smooth, and slightly depressed along its centre. In the 

 ventral valve the sinus is regularly concave and smooth, each valve being orna- 

 mented with from sixteen to thirty rounded or flattened ribs. 



This species appears to be rare in Scotland, for I am acquainted with but a 

 single small example, which was derived from carboniferous limestone to the 

 north of Glasgow, and now belongs to the Museum of Practical Geology. It 

 measures eleven lines in length by twelve in breadth and ten in depth. 



XII. — Spieipeea ovalis. Phillips. PL xii., figs. 26, 27. 



Sjnrifera omlis, Philips, Geol. of York., vol. ii, p. 219, pi. x., fig. 5, 1806 ; and 

 Dav. Mon. Garb., p. 53., pi. ix., figs. 20—26. 



This shell is, transversely or elongatedly oval, with a very short hinge-line, 

 and rounded cardinal angles ; the area is triangular, and more often ^Yider than 

 high. The dorsal valve is moderately convex, and much less deep than the 

 opposite one, with a smooth, broad, flattened, mesial fold. In the ventral 

 valve the beak is small, tapering, and incurved ; the sinus rather shallow, com- 

 mencing at the extremity of the beak, it extends to the front and is orna- 

 mented with one or two longitudinal ribs placed on either of its sides. Prom 

 eighteen to twenty simple flattened ribs ornament the surface of each valve. 

 Sp. 01- alls appears to be an uncommon species in Scotland, and to which Prof. 

 Pleming, in 1828, had applied the name exarata ; but as the last named author 

 never figured his shell, and that the description, "Perforated valve, with broad, 

 smooth, flattened ribs, divided by shallow, narrow furrows ; beak gibbous, in- 

 curved ; hinge very short," might apply equally Avell to several other species, 

 I should question the propriety of adopting the term exarata (notwithstanduig 

 its priority of date) in preference to the well-known one by Phillips, and 

 especially so as Dr. Eleming further observes that, although he has frequently 

 found the perforated valve, it was always mutilated or without the other valve, 

 with which he was not acquainted, as may be seen from the origuial fragment 

 represented in our plate, and which was kindly communicated by the author. 



8p. ovalis has been found in the Corrie Burn beds, Stirlingshire; also in West- 

 Lothian and at West Broadstone in Ayrshire. In Lanarkshii'e at Brockley, 

 near Lesmahago. 



XIII. — Spirifera glabra. Martin. PI. xii., figs. 32 — 34. 



Conchyliolithus anometes glaber, Martm Petrif. Derb., pi. xlviii,, figs. 9, 10, 1809, 

 and Dav. Mon. Garb., p. 59, pi. xi., figs. 1 — 9, pi. xii., figs. 1 — 5, 11, 12. 



This shell varies to such an extent, that it is difficult to assign any perma- 

 nent character ; the shape is, however, more often transversely oval, and rarely 

 longer than wide. Both valves differ in degree of convexity, the ventral one 

 being generally the deepest. The hinge-luie is shorter than the greatest width 

 of the shell, with rounded cardhial angles and the beak more or less approxi- 

 mate and incurved. 



The ventral hinge area is triangular and of moderate dimensions, the dorsal 

 one being narrow and sub-parallel, the mesial fold is either slightly and evenly 

 convex, rising gradually from the lateral portions of the valve, or abruptly 

 elevated with a longitudinal depression along its middle ; the sinus varies like- 

 wise in depth according to the specimens. Externally both valves are gene- 

 rally smooth, but sometimes a few obscurely marked flattened ribs may be 

 observed on the lateral portions of the shell. 



Tliis species, at times, attains thirty-two lines in length by forty-three in 

 width, and twenty-six in deptli ; but no Scottish specimens I have hitherto 

 seen attain half those proporhons. 



At Harestanes and Langshaw Burn in Lauarkshii'C, Sp. glabra is found at 



