202 BRITISH PALASOZOIC FOSSILS. [ Bracuiopopa. 
curvature, crossed at nearly regular intervals by sharp scaly lines of growth. Casts shew, in the flattened 
entering valve, a small pit each side of the beak for the cardinal teeth, and a shallow mesial sulcus ex- 
tending half way to the margin, produced by a mesial septum; in the large receiving valve, two short, 
oblique, diverging slits of the dental lamelle bordering the beak. Width four lines, proportional length of 
receiving valve “, length of entering valve slightly less, depth j{;; tissue of shell fibrous. 
As some modern writers have referred this shell to the genus Orthis, I have taken great pains to 
ascertain the characters of the hinge, as the obvious absence of the puncturing in the tissue of the shell 
rendered the reference to Orthis very doubtful in my mind; and I have convinced myself that there is no 
cardinal area whatever, but that the beak of the entering valve is simply pointed, scarcely incurved, while 
that of the receiving valve is pointed, hollow, and so much incurved only as to leave a wide triangular fora- 
men beneath it; the hinge-characters therefore warrant the placing this singular shell in Hemithyris, with 
which also its tissue is identical. 
Position and Locality —Abundant in the fine Bala sandstone of Pwllheli, Caernarvonshire ; abundant in 
the coarse sandstone and conglomorate near Presteign, Radnorshire; common in the fine sandstone of the 
Braes, one and half miles EK. of Girvan, Ayrshire (common southern yariety). 
Var. Scorica (M°Coy). Pl. 1. H. fig. 10. 
Ref.— Quart. Geol. Journ. August, 1851, t. 9. f. 12. 
This may ultimately prove a distinct species, in which case the varietal name may become specific. 
It is distinguished from the type species by the ribs being more numerous (usually about twenty to twenty- 
four), considerably narrower, less prominent, and less regular in size and directness, and often irregularly 
forked—a character seldom or never seen except at the inner edge of the flat valve in the typical specimens. 
The receiving valve is also slightly more carinate, and the entering valve not so perfectly flattened, and with 
a faint trace of a wide, undefined, mesial hollow. 
This Scotch variety closely approaches M. de Verneuil’s figure of the Producta eminens of Pander, which 
he considers a variety of P. obtusa, Pand., and places in the genus Orthis. This Orthis obtusa has been 
shewn by de Verneuil to want the cardinal area of Ovthis, and is clearly congeneric with our present species, 
which seems to differ from the var. eminens by having fewer ribs, being less tumid, particularly in the 
entering valve, having no distinct muscular internal impressions; and from all the varieties, by having the 
front narrower or more convex, and the hinge-line shorter. A comparison with abundance of Russian 
specimens might obliterate some of these differences. 
Position and Locality—This variety is extremely common in the greenish sandstone of Mullock, Dal- 
quorhan, near Girvan, Aryshire. 
Explanation of Figures —P\. 1. H. fig. 10. Natural size, entering valve; 10a, Ditto, receiving valve ; 
104, Ditto, view of front margin. 
HeMmITHYRIS LACUNOSA (Linn. Sp.) 
Ref. and Syn.= Terebratula lacunosa Schlot. Nachtrage, t. 10. f. 6. = 7". borealis id. Kat. 65; Sil. Syst. 
tH UDA 3 UO, 
Sp. Ch.—Transversely oval, or subtrigonal, very gibbous, entering valve most so; sinus in front margin 
quadrate, very deep, abruptly defined, but the mesial ridge scarcely elevated, except at the margin, and the 
corresponding wide, flat, mesial hollow extending two-thirds to the beak ; six or seven strong, angular, simple 
ridges on each side, those nearest the angle short, leaving an obscurely defined smooth space on each side of 
the beak; mesial ridge with four angular ridges, equal to the lateral ones in size for about five lines from the 
beak, where the outer pair dichotomise, forming six large equal ridges at the margin of large specimens, and 
five ribs in the mesial hollow ; surface nearly smooth, or crossed by minute, regular, transverse striae. Width of 
large specimen one inch one line, proportional length \3, length of entering valve 7, depth of both valves ;7; 
tissue of shell fibrous. 
