a a 
ORTHIDZ. 217 
lesser size and height. Surface of both valves covered with numerous thread-like stric, 
which increase in number by many interpolations, while the whole surface is crossed 
at intervals by concentric lines of growth. Interior not known. 
Length 5, width 5, depth 33 lines. 
Obs. This small species seems distinguished from its congeners by its circular form, 
the great and regular convexity of its dorsal valve, and apparent total absence of either 
fold or sinus. It was found by Mrs. Gray, of Glasgow, in the Caradoc Limestone of 
Craig Head Quarry, Girvan, Ayrshire. I am not acquainted with the shell from any 
other locality. 
Ortuis BASALIS, Da/man(?). Pl. XXVII, figs. 10, 11. 
OrtHIs BASALIS, Dalman. Vet. Akad. Handl., p. 116, pl. i, fig. 5, 1827. 
— —  fHisinger. Letheea Suecica, p. 71, pl. xx, fig. 12, 1837. 
— ?— Von Buch. Ueber Delthyris, p. 60, 1837. 
—  ELEGANTULA, Dav. London Geol. Journal, p. 62, pl. xiii, figs. 10, 11, 1847. 
— — Lindstrém. Gotlands Brachiopoder, p. 367, 1860. 
Spee. Char. Almost circular, slightly longer than wide, broadest posteriorly, sides 
rounded, gently converging anteriorly towards the front; hinge-line a little less than the 
ereatest width of shell ; dorsal valve very slightly convex, or almost flat, with a shallow 
median depression, which, commencing close to the umbone, extends to the front. Ventral 
valve moderately convex, somewhat longitudinally keeled along the middle ; area triangular, 
of moderate height, fissure open; beak very small, incurved, projecting but little above 
the area. Surface of valves marked by numerous small, radiating, bifurcated and inter- 
polated, raised striae, crossed by concentric lines of growth. In the interior of the dorsal 
valve a small bilobed cardinal process is situated between two small, curved, deviating, 
_ projecting brachial processes, while a moderately wide, rounded mesial ridge separates the 
two pair of adductor muscular impressions. 
Length 8, width 9, depth 3 lines. 
Obs. The Swedish types of this species have not been hitherto properly or sutti- 
ciently illustrated, so that it is difficult to be perfectly certain as to its occurrence m 
Britain. Dr. Lindstrém, to whom I had sent specimens of the shell figured in our plate, 
assured me that it was referable to Dalman’s O. Jasalis ; and we are informed by Baron 
von Buch, as well as by Dr. Lindstrém, that Dalman’s species does not always present the 
heart-shaped form given to it by the last-named naturalist ; but I would at the same time 
observe that I doubt greatly that the shell figured by Von Buch as O. dasalis does really 
belong to that species. 
Dalman states, in his description, that this species is nearly allied to O. e/e- 
gantula, but distinct, being less gibbous, and manifestly broader anteriorly ; the beak 
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