Bracuropopa.] LOWER PAL/EOZOIC MOLLUSCA. 207 
HeMITHYRIS SUBUNDATA (M/°Coy). Pl. 1. H. fig. 9. 
Ref.—id. M°Coy, Ann. Nat. Hist. 2nd Series, Vol. VIII. p. 394. 
Sp. Ch.—Transversely broad-oval; valves gently and almost equally convex ; beaks very small, apical 
angle 140° near the apex, lateral margins straight, front raised into a rounded wave, from which in the large 
valve a wide shallow mesial depression extends half way to the beak, with a corresponding elevation in the 
small valve, in some specimens faintly extended to the beak; surface smooth. Average width one inch, pro- 
portional length ;;, length of entering valve =, depth of both valves = to =. 
This species is flatter and less wide than the Atrypa (Pentamerus) undata (Sow.), but less long than the 
Atrypa (Pentamerus) lens, being intermediate in form between the two; the casts shew however in the small 
valve a rather strong slit in the beak for the short medial septum, and a transverse pit on each side for the 
origin of the apophyses or hinge-teeth. The receiving valve has two short diverging dental lamellz bordering 
its beak, as in Hemithyris, with one or two small ridges between them; the sides of both valves shew about 
three straight once or twice-branched ridges of the pallial and ovarian vessels. The very small beak separates 
it from the Terebratula Herculea (Bar.) 
Position and Locality —V ery common in the schists and limestone of Mathyrafal, S. of Meifod, Mont- 
gomeryshire, and in the schists of Pen y Craig, Llangynyw, Montgomeryshire; slate of Alt ffair ffynnon, 
Llanfyllin, N. Wales. 
Explanation of Figures —P\. 1. H. fig. 9. Natural size from the limestone of Mathyrafal, shewing the 
smooth shell partially removed, exposing the dichotomous impressions of the pallial vessels; 9a, profile of 
rostral portion ; 9 4, end view of internal cast ; 9c, front view, shewing the elevation of the margin. 
Hemiruyris Upstton (Bar. Sp.) 
hef. and Syn.= Terebratula id. (Barrande, Naturwissenschaft Abhandl. Vol. I. t. 15. f. 9). 
Sp. Ch.—Subpentagonal, depressed; apical angle 90°; valves almost equally convex, greatest width 
about the middle of the length, front narrow, with a rounded notch in the middle, from whence a deep 
narrow depression extends two-thirds to the beak in the receiving valve ; entering valve evenly convex, or 
slightly depressed in the middle of the front margin; surface smooth. Length seven lines, proportional 
width =, length of receiving valve =, depth of receiving valve alone %. 
I have only seen the large valve of the British specimen, but in the Bohemian the small valve has 
only a marginal depression instead of the long sulcus of the opposite one. It is considerably wider than 
the 7. canalis (Sow.), and longer and more depressed than the 7’. didyma (Dal.) 
Position and Locality—tIn the sandy schists of Pwllheli, Caernaryonshire, 
Hemituyris Witsont (Sow. Sp.) 
Ref. and Syn.=Terebratula id. Min, Con. t. 118. f. 3; Sil. Syst. t. 6. f. 7. 
Sp. Ch.—Subpentagonal when young, apical angle 110°, with valves evenly tumid, becoming semi- 
cylindrical with age, by the abruptly deflected vertical extension of the front, with nearly parallel sides; a 
space about three to four lines long round the beak nearly smooth in both valves, but after this length 
(when the abrupt deflexion of the margin commences) about forty-eight equal, obtuse, longitudinal ridges, 
suddenly appear (about six in two lines) in middle of front, each of which becomes flattened, and divided 
by a fine mesial sulcus; commissure of the valves nearly straight at the sides, abruptly raised into a very 
deep oblong sinus in front, which gives very slight or no trace of mesial ridge or hollow in most specimens. 
Length of small specimen five lines, width the same, depth of both valves “. In older specimens the 
depth of both valves exceeds the length by one-third. The muscular impressions in the casts of receiving 
valve forming a very prominent subpentagonal boss. 
Position and Locality——Very common in the Aymestry limestone of Sedgley, Dudley, Staffordshire ; 
in Upper Ludlow rock, right bank of Dee, near Llangollen; Aymestry limestone of Leintwardine, Shrop- 
