198 BRITISH PALAOZOIC FOSSILS. [ Bracutopopa. 
and a trace of a small mesial septum, and the slits of the wide, slightly diverging, dental lamelle, bordering 
the beak of the receiving valve) ; tissue of the shell fibrous. 
This species varies considerably, but is easily distinguished by its strong branching scaly ribs and sharply 
defined mesial fold; from the dichotomising of the lateral ribs they often seem fo arch outwards; the 
figure in the Silurian System is considerably longer, and Dalman’s figure rather wider, and with more pro- 
minent beak, than the usual forms. 
Position and Locality——In the Wenlock limestone of Wenlock, Shropshire; in the caleareous Upper 
Bala beds of Pont y Glyn, Diffwys, W. of Corwen, Merionethshire; Upper Bala sandstone of Alt Goch, 
Llanfyllin, Montgomeryshire ; Upper Bala schists of Rhosfawr, N. of Glog, Llanfyllin, N. Wales; fine sandy 
Bala schists of Tre Gib, S. of Llandeilo. Variety with much branched ribs in the schists of Pen y Craig, 
Llangynyw, Montgomeryshire ; Bala limestone of Mathyrafal, S. of Meifod, Montgomeryshire ; in the olive 
schists W. of Llanfyllin, Montgomeryshire; in the fine Bala sandstone of Alt yr Anker, Meifod, Montgo- 
meryshire ; sandy schists of Goleugoed, Llandovery, Mandinam, Caermarthenshire (very wide variety) ; Upper 
Bala schists of Blaen y Cwm, W. of Nantyr, Glyn Ceiriog, Denbighshire; schists of Gelli Grin, Bala, 
Merionethshire. 
SPIRIGERINA RETICULARIS (Linn. Sp.) 
Ref. and Syn.= Anomia reticularis Linn, Syst. Nat.=Terebratula prisca Schlot.= 7. eaplanatus Schlot.= 
Terebratula affinis Sow. Min. Con. and Sil. Syst. t. 6. f. 5.= A. aspera Sow. Sil. Syst. t. 12. f. 5. (not of 
Dal. nor Schlot.) = 4. orbicularis Sow. Sil. Syst. t. 19. f. 3, 4. 
Sp. Ch.—Elongate, ovate, or sub-triangular from the hinge-line extending into compressed ears as wide 
as the shell (small varieties often nearly orbicular) ; in ordinary adult specimens the receiving valve is nearly 
flat, convex at the beak, which is small and prominent, becoming gradually concave towards the margins, which 
are more or less reflected ; the opposite valve very gibbous along the middle, gradually sloping towards the 
margin, surface covered with strong rounded or subangular strix, irregularly branching and increasing in 
thickness towards the margin, separated by deep sulci rather less than the ridges in width, both crossed by 
irregular, strong, scaly lines of growth, averaging five or six in two lines, at six lines from the beak (varying from 
four to seven). Length one inch two lines, width the same, proportional depth of both valves ,{; to 7: in 
specimens four lines long the valves are evenly convex and nearly orbicular; the entering valve little more 
tumid than the receiving one; cast of the beaked valve shewing a deep oblique pit, on each side of the beak for 
the hinge-tooth ; a large, broad oval muscular impression, faintly divided down the middle and obscurely radiated, 
occupies the middle of the rostral half, round this is a space closely set with small irregular papillee (much smaller 
than in Barrande’s figure, Naturwissenschaftliche Abhandlungen, Vol. 1. t. 19. f. 9), probably indicating thick 
fleshy cirri of the mantle, traversed by one thick trunk on each side giving branches obliquely up and down, 
probably indicating the place of the ovaries ; external margin smooth. 
This is a very variable shell, but the above description indicates the most common and characteristic 
variety. It varies, Ist, in the convexity of the valves, both as to degree, distance from the beak at which it is 
greatest, and equality, some small varieties, and the young at all times, having the valves almost equally and 
evenly convex; 2nd, in form, some, particularly the young and the small varieties, being nearly orbicular, others 
being elongate and nearly triangular from the width of the hinge-line and narrowness of the front; 3rd, in the 
number, thickness, and closeness of the ridges, and the scales which cross them, both of which are often 
smaller, and closer than the the above-described typical variety. I could not trace any connexion between 
these varieties and their geological position ; there being not the slightest difference between the series of 
varieties in the different parts of the Cambrian, Silurian, and Eifel rocks. 
Position and Locality—In the Lower Ludlow rock of Leintwardine, Shropshire ; common in the Wen- 
lock limestone of Sedgley, near Dudley, Staffordshire, and Wenlock, Shropshire, and Dudley, Staffordshire ; 
Upper Ludlow rock of Collin field, Kendal, Westmoreland ; olive schists of Parklane, Llandeilo, above the 
white grits; flags of Middleton Park, Caermarthenshire ; schists of Coed Sion, near Llangadoc, S. Wales ; 
olive Ludlow rock of Mynydd-y-Gaer S. side, Llanefydd, near Ruthin, Denbighshire ; abundant in the schists 
