ORTHID . 223 
Ortuis FALLAX, Salter. Pl. XXXI, figs. 9—11. 
ORTHIS FALLAX, Salter. Addenda to Synopsis of Sil. Foss. of Ireland, p. 72, pl. v, 
fig. 3, 1846. 
— — Ibid. Siluria, 2nd ed., p. 544, 1859. 
Spec. Char. 'Transversely oval, wider than long; hinge-line slightly shorter 
than the width of shell. Dorsal valve semicircular, moderately convex, fold wide, 
raised in front. Ventral valve moderately convex, most so at the beak; a wide 
depression or sinus commences at a short distance from the extremity of the beak, 
and extends to the front. Area narrow, fissure open, beak slightly incurved. Surface 
of both valves marked by numerous radiating thread-like strie, increasing in number 
towards the margin by means of numerous interpolations. In the interior of dorsal valve 
a small cardinal process is situated between two small, curved, brachial processes. In the 
interior of ventral valve the muscular depression is elongate-oval, rather small, and 
divided longitudinally by a narrow median ridge. 
Length 7, width 8 lines. 
Obs. Of this species (?) I have not been able to obtain sufficient or quite satisfactory 
material, but, thanks to the kindness of Sir R. Griffith, I have been able to examine and 
_ figure the specimens from which Mr. Salter described and illustrated his species. These 
consist of two or three internal casts and external impressions, no complete example 
having been hitherto discovered. Consequently I am not quite certain whether this is a 
good distinct species, or a variation in shape of the preceding one, as has been supposed 
by Prof. M‘Coy. The hinge-line is, however, much longer than what we find in either 
O. reversa or the var. (?) Mullockiensis ; the ribs are likewise rather coarser, and the mus- 
cular impressions smaller and somewhat different in shape. 
Position and Locality. In ‘Siluria’ Mr. Salter refers O. fallae to the Llandovery 
period. In Ireland it occurs at Killey, Pomeroy, County Tyrone ; it has also been found 
in the Caradoc at Desertcreat, Tyrone (Survey Mus.). Mr. Salter informs me that 
internal and external casts abound in a sandstone of the Llandovery age in Galway, and 
that a species much resembling it also occurs in Ayrshire. 
Orruis Baityana, sp. nov. Pl. XXIX, figs. 19—20. 
Spec. Char. Shell thick, round, slightly wider than long; valves moderately convex ; 
hinge-line shorter than the width of shell; areas small, fissure in both valves open and 
large. Exterior surface marked by numerous fine, thread-like, radiating striz, here and 
there crossed by concentric lines of growth. In the interior of ventral valve a prominent 
tooth on each side of fissure. The dental plates enclose an elongated muscular depression 
of about six lines in length by some four in breadth, somewhat elevated and angular 
