Bracuropopa.] LOWER PALAZOZOIC MOLLUSGCA. 205 
not co-existing, sometimes the one, and sometimes both being observable in the contiguous specimens, which 
are clustered in great numbers in the Upper Ludlow rock; and the obtuse looking examples (nucula) often 
prove, on counting, to have the same number of ridges, and to have the same proportions as the sharply- 
marked ones (pulchra). 
Position and Locality.—V ery abundant in the Upper Ludlow rock of Burton and Brockton, near Wenlock ; 
abundant in the green quartzose Upper Ludlow rock of Collinfield, and Benson Knot, Kendal, Westmoreland ; 
in the fine Ludlow rock above Parklane, Llandeilo, (above the white grits) ; Upper Ludlow of Downton Castle, 
Aymestry, Herefordshire; Lower Ludlow of Leintwardine, Shropshire ; Upper Ludlow of Dinas Bran, 
Llangollen, Denbighshire; in ditto, Lambrigg Fell, Kendal, Westmoreland; in hard gritty ditto, near Llan. 
gollen, Denbighshire ; in the olive schists of Mynydd y Gaer, Llanefydd near Ruthin, Denbighshire ; schists of 
Cwm Craig Ddu, Builth, Radnorshire; Aymestry limestone of Mortimer’s Cross, Aymestry, Herefordshire ; 
Wenlock limestone of Sedgley, near Dudley, Staffordshire ; limestone of Balmae Shore, Kirkcudbright ; Braes, 
one and half mile E. of Girvan, Ayrshire; abundant in Upper Ludlow rock of Woolhope. 
HEMITHYRIS PENTAGONA (Som. Sp.) 
Ref. and Syn. = Terebratula pentagona Sow. Sil. Syst. t. 5. f. 22. 
Sp. Ch.—Obscurely pentagonal, very much depressed, margins sharp; apical angle 115°; beak of 
entering valve pointed, slightly curved ; lateral margins nearly level, anterior margin slightly raised into a 
very wide and shallow sinus, from which the mesial ridge and hollow are very slightly indicated for a 
short distance from the margin; surface radiated with about thirty obtuse, narrow, unequal, occasionally 
branched ridges, about eight of which correspond with the mesial sinus in a specimen four and half lines 
long, and all of which become indistinct at two or three lines from the beak. Width of rather small specimen 
five lines, proportional length of receiving valve =, of entering valve 4, depth of both valves +4; substance 
fibrous. 
Position and Locality—Rare in the limestone of the Hollies, Church Stretton, Shropshire. Rare in the 
limestone of Clungunford, Shropshire. 
? HEMITHYRIS PISUM (Sow. Sp.) 
Ref. and Syn. = Spirifer ? pisum Sow. Sil. Syst. t. 13. f. 9. 
Sp. Ch.—Suborbicular, beaks very small, scarcely projecting ; front slightly narrowed, and with a minute 
obsolete sinus, not raising the edge; valves nearly equal, both gibbous a little behind the middle, gradually 
becoming depressed towards the sharp edge; a faint linear mesial sulcus extends from the beak of each 
valve to the sinus in the middle, coinciding posteriorly with a long internal mesial septum in each valve ; 
beak of the receiving valve very slightly prominent, with a wide triangular opening beneath the apex. Width 
three lines, proportional length about ;;;, depth of both valves about =. 
I have ascertained by carefully breaking a specimen, that there are no internal spiral appendages, and 
therefore the species does not belong to Spirifer, and I have observed a large triangular opening beneath 
the beak, so that it does not belong to Atrypa, where M. d’Orbigny has placed it. 
Position and Locality—Not uncommon in the Wenlock limestone of Wenlock, Shropshire. 
HEMITHYRIS ROTUNDA (Sow. Sp.) 
Ref. and Syn.= Atrypa rotunda Sow. Sil. Syst. t.13. f. 7. 
Sp. Ch.—Ovate, very gibbous, valves nearly equally convex, beak moderate, apical angle 115°, lateral 
margins nearly straight, front margin raised into a wide trilobed wave, from which three short, broad, 
obseure ridges extend half way towards the beak. Width about five lines, proportional length “, depth 
of both valves 4. 
