Bracuropopa. | LOWER PALZOZOIC MOLLUSCA. 221 
incurved slit of two smaller lateral ridges ; division of the anterior pair from the posterior very slightly marked, 
we latter largest; surface closely granulo-punctate ; average width six and a half lines, proportional length 
length of entering valve {, depth of both valves 5. 
The great depression and near equality of the valves, much finer striz, and singular elongate, narrow 
form of the muscular impressiuns in the entering valve, as well as the slightly-divergent, slender, hinge- 
teeth of the entering valve, and width of the subsinuate front, easily distinguish this species from the 
O. elegantula. 
Position and Locality.—Very common in the Upper Ludlow rock of Woolhope; abundant in the 
schists and limestone of the Upper Ludlow rock of Downton Castle, near Ludlow, Shropshire; schists of 
Dinas Bran, Llangollen, Denbighshire; schists of Keepers Lodge, Goldengrove, Llandeilo, Caermarthen- 
shire; Upper Ludlow sandy flags of Benson Knot, Kendal, Westmoreland; var. in the Lower Ludlow 
schists of Erw Gillfach, Builth, Radnorshire; Upper Ludlow rock, near Ludlow, Shropshire; Upper Ludlow 
limestone of Kington, Herefordshire; Upper Ludlow limestone of Mortimer’s Cross, Aymestry, Herefordshire ; 
Ludlow mudstone of Parklane, Ludlow, Shropshire; Ludlow limestone of Leintwardine, Shropshire. 
im 
OrtHis PARVA (Pander. Sp.) 
Ref. and Syn. = Orthambonites parva Pander, Beitr. zur Geogn. Russl. t. 26. f. 10.= Orthis parva + O. avellana 
M. V. K. Geol. Russ. t. 13. f. 3 and 4. 
Sp. Ch—Obovate, or rotundato-quadrate, front often obtusely pointed in small very convex specimens, 
or wide and flattened in depressed ones; receiving valve very tumid along the middle, profile much curved, 
greatest depth about one-third of the length from the beak, sides sloping from the middle line, with little 
convexity to the margin, beak large, much incurved to the level of the lateral margins; entering valve 
gently convex about half the depth of the other, with a narrow mesial depression near the beak, gradually 
widening towards the front margin; cardinal area small in the entering valve, moderately high, triangular, 
curved, eed very much inclined backwards in the receiving valve ; fine line slightly less flan the width 
of the shell; both valves radiated with strong, sharply angular, amas irregularly fasciculated ridges, 
very frequently dichotomising, and increasing in number also by intercalation towards the margin, arched 
towards the cardinal angles at the sides; the irregular multiplication of the ridges distinct at one or two 
lines from the beak, at which latter size there are fifteen to nineteen ridges in two lines, about thirteen 
in two lines at the lateral margin of large specimens six lines long; interstices strongly marked with 
transverse imbricating granules. | Average width five lines, proportional length of receiving valve “, of 
entering valve ;;,, depth of both valves =. 
In the sharp, angular, fasciculated character of the striation, the large specimens in particular approxi- 
mate to the O. testudinaria; but as the greater number of specimens of O. parva are little more than 
three lines long, it will be seen by the great number of the ribs in a given space, and their complex 
fission, that they differ totally from the young specimens of O. testudinaria. or from the ridging at the 
same distance from the beak of old specimens thereof. Some specimens in certain states of preservation, 
where the fasciculation is obscured, and the strize unusually numerous (forming the var. avellana of M. V.K.), 
very strongly approximate the var. a. antiquior of the O. elegantula, which, however, has always more equal, 
obtuse, less-branched strive; their equality in thickness and prominence, particularly at the margin, con- 
trasting strongly with the present species. 
Position and Locality—Common in the Bala schists of Llansantfraid, Glyn Ceiriog, Denbighshire ; Bala 
sandstone of Ardwell, S. of Girvan, Ayrshire; Bala schists of Gelli Grin, Bala, Merionethshire; Bala schists 
of Cader Dinmael, near Corwen, Denbighshire; Bala schists of Llanfyllin, Montgomeryshire; calcareous 
Bala schists, Carnedd fawr, S. of Bala, Merionethshire; Bala schists of Maes Meillion, S. of Bala, Merio- 
nethshire; Bala schists of Bryn Melyn, near Bala, Merionethshire; Bala schists of hills N. of Moel 
Uchlas, Montgomeryshire ; schists in stream above Llanfwrog, near Ruthin; calcareous Bala schists of Dinas 
Mowddy, Merionethshire; Bala schists of Rhiwargor, near Llanwddyn, Montgomeryshire; Bala schists of 
