324 BRITISH SILURIAN BRACHIOPODA. 



sometimes forming small scmicylindrical ears ; sides rounded ; front almost straight. 

 Ventral valve convex, most so at and near the beak, which is incurved and of very small 

 projection; area moderately w^ide; fissure narrow, arched over by a pseudo-deltidium. 

 Dorsal valve concave, following the curves of the opposite valve ; hinge-area narrow. 

 Surface of valves ornamented with numerous fine, equal, hair-like, rounded radii ; with 

 interspaces between each pair, four times as great as the width of each of the principal 

 riblets ; the interspace is itself longitudinally furrowed by five to seven very fine striae, 

 which are again separated by very narrow sulci, containing rows of minute punctures. 

 In the interior of the ventral valve the elongated, deviating, muscular depressions are 

 posteriorly divided in the middle by a median ridge ; anteriorly by a deep indentation. 

 In the interior of the dorsal valve the muscular scars form two large, wide, flattened, 

 parallel, slightly raised depressions, separated into two pairs by a deep median interspace, 

 along the centre of which is a small ridge. 

 Length 5, width 9, depth 1 line. 



Obs. This species seems to differ from L. transversalis chiefly by its smaller beak, 

 more transverse form, coarser strige, and much finer punctures ; but especially by the 

 expanded flattened shape (instead of convexity) of its muscular impressions. This 

 difference becomes at once apparent on a comparison of the interior of the dorsal valve 

 of both species drawn in our plate (figs. 7 and 16). The interspace between the 

 principal radii is also comparatively smaller in this species than in Lept. transversalis ; 

 and the longitudinal striae are likewise fewer in number. 



Position and Locality. In ' Siluria ' L. sericea is stated to occur in the Llandeilo, 

 Caradoc or Bala, Llandovery, and perhaps the Wenlock formation. In the Caradoc it is 

 especially abundant ; and half of a quarto page of M'Coy's work on ' British Palaeozoic 

 Fossils ' is devoted to their enumeration. We will mention a smaller number of the 

 principal localities. 



In the Llandeilo Flags at Llan Mill. 



In the Caradoc at Pwll-y-wrach-isaf ; Hope Bowdler ; Acton Scott ; Y-GeUi 

 Grin ; Bala ; Carnedd Dafydd ; Bettws-y-Coed ; Dolwyddelan ; Bodean ; Pwllhei ; 

 Llyn Idwal, Caernarvonshire. South of Cerrig-y-Druidion ; south of Llangollen ; 

 Cricor Mawr ; east of Llanelidan ; south of Pont-y-Glyn Diffwys, Glyn Ceiriog, Denbigh- 

 shire. Llanwddyn ; Meifod ; Llanfyllin ; north of Llangedwin ; Alt-yr- Anker, Mont- 

 gomeryshire. East, west, and south-east of Bala Lake, &c., Merionethshire, &c. 

 Common also in Bala beds at Coedog, Corwen ; Das Eithen ridge ; Hirnant ; Haver- 

 fordwest ; and elsewhere in Wales; at Whittingslow, Horderley, and Moclydd near 

 Oswestry, in Shropshire ; and at Keisley and Pusgill, near Dufton, Westmoreland. 



In the Lower Llandovery at Miomffri ; half a mile south-east of Cwmrhyddan, Cefn- 

 rhyddan, Llandovery, Mathyrafal, &c. 



In Tipper Llandovery at Pen tan, Coldbrook, Craig-yr-Coyddon, Llandovery, &c. 



I am not acquainted with any Wenlock localities. 



