18 
Till-: GEOLOGIST. 
wide and produced, smooth, and slij^lilly depressed along its centre. In the 
ventral valve the sinus is ref^ularly concave and smooth, each valve being orna- 
mented with from sixteen to thirty rounded or ilattened 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 tlic 
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.— Spirtfera ovalis. Phillips. PI. xii., figs. 20, 27. 
Spirifera ovalis, Philips, Geol. of York., vol. ii, p. 219, pl. x., fig. 5, 1806 ; and 
Dav. Mon. Garb., p. 53., pl. ix., figs. 20— 2G. 
This shell is, transversely or elongatedly oval, with a very short hinge-line, 
and rounded cardinal angles ; the area is triangular, and more often wider tlian 
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 tlie beak is small, tapering, and incurved ; the sinus rather sliallow, 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 sm-faee of each valve. 
Sp. ovalis a})pears to be an uncommon species in Scotland, and to which Prof. 
Pleming, in 1828, had ap})lied the name exarata ; but as the last named autlior 
never figured his shell, and that the description, " Perforated valve, with broad, 
smooth, flattened ribs, divided by sliallow, narrow furrows ; beak gibbous, in- 
curved ; liinge very short," might apply equally well to several other species, 
1 should question the propriety of adopting the term exarata (notwithstanding 
its priority of date) in preference to the well-known one by Phillips, and 
especially so as Dr. Fleming further obsenes 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 original fragment 
represented in our plate, and wliieh was kindly communicated by the author. 
Sp. ovalis has been found in the Corrie Burn beds, Stirlingshire ; also in West- 
Lothian and at West Broadstoue iii Ayrshii-e. In Lanarkshii-e at Brockley, 
near Lesmahago. 
XIII. — Spirifera glabra. Martin. Pl. xii., figs. 32 — 34. 
Conchyliolithus anometes glaber, Martin Petrif. Derb., pl. xlviii., figs. 9, 10, 1809, 
and Dav. Mon. Garb., p. 59, pl. xi., figs. 1 — 9, pl. xii., figs. 1 — 5, 11, 12. 
This sheU varies to such an extent, that it is difficult to assign any perma- 
nent eliaracter ; 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-line is shorter than the greatest width 
of the shell, with rounded cardinal 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 abru]itly 
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. 
This species, at times, attains thirty-two lines in length by forty-three in 
width, and twenty-six in depth ; but no Scottish specunens I have liithcrto 
seen attain half those proportions. 
At Harestanes and Langshaw Burn in Lanarkshire, Sp. t/lahra is found at 
