326 BRITISH SILURIAN BRACHIOPODA. 



cylindrical ears. Ventral valve gibbous, much arched in profile, flattened at the ears ; 

 area narrow^ ; fissure covered by a pseudo-deltidium. Dorsal valve concave, following 

 the curves of the opposite valve ; area narrov^^. External surface ornamented with four or 

 five slender, thread-like, rounded radii, with broad interspaces finely and longitudinally 

 striated. In the interior of the ventral valve a prominent tooth on each side of the fissure 

 is supported by dental plates, which enclose a moderate-sized saucer-shaped muscular 

 depression, with raised edge ; longitudinally divided by a prominent median ridge, and 

 deeply indented in front. In the interior of the dorsal valve the muscular depressions 

 are large, elongated, and divided into four parallel lobes, margined by a raised rim. 

 Length 2, width 4, depth ^ line. 

 Obs. This small species was named, but not described or figured, by Mr. Salter. I 

 have described and drawn the shell from the typical specimens in the Museum of Practical 

 Geology. It occurs chiefly in the condition of internal casts ; and the enlarged figures, 

 22 a and 23 a, show well its characters ; as also do the enlarged figures of the shell itself, 

 24 a and 25 a, taken in gutta-percha from internal casts. From figs. 22 and 24 it will be 

 seen that the muscular depressions are wider in some examples than in others. There are 

 also four longitudinal indented lines or vascular impressions seen in the cast of the ventral 

 valve, which give it a very peculiar appearance (fig. 23 a). 



I cannot say whether this species is distinct from Leptcena qiiinqiiecostata, as I am not 

 acquainted with the internal characters of the last-named species ; but it was stated to be 

 so by Mr. Salter. 



Position and Locality. In ' Siluria ' this species is restricted to the Llandovery period ; 

 but specimens in the Museum of Practical Geology are labelled from the Caradoc of 

 Sholes Hook, Haverfordwest ; Bettws-y-Coed, Caernarvonshire ; east and west of Bala 

 Lake, Merionethshire, &c. 



In the Lower Llandovery at the Gas Works, Haverfordwest ; west of Pantygasey, 

 Llandovery, &c. 



In the Upper Llandovery at Builth ; Cefn-Craig-Gwyddon ; Mathyrafal ; Pentan ; 

 Norbury ; Bishop's Castle, &c. 



I am not acquainted with any Scottish examples. 



In Ireland it is found in the Caradoc at Desertcreat, &c. 



Lept^na tenuicincta, M'Coy. (sp.). PI. XLVII, figs. 7 — 18. 



Producta tenuicincta, MCoy. Sil. Foss. Ireland, p. 25, pi. iii, fig. 4, 1846. 

 Lept^na enigma, De Verneuil. Bull. Soc. Gcol. France, ser. 2, vol. v, p. 340, pi. ir, 

 fig. 6, 1848. 



— tenuicincta, M'Coy. Brit. Pal. Foss., p. 239, pi. i h, fig. 40, 1852. 



— — Salter. Siluria, 3rd ed., p. 210, fig. 4, 1859. 



— — Id. Mem. Geol. Survey, vol. iii, p. 267, 1866. 



