156 



BRITISH SILURIAN BRACHIOPODA. 



Pentamerus. I observe," he adds, " that in those species in which the plates are very 

 small the outwardly curved marginal portion of the two diverging plates in the beak of 

 the entering valve is unusually strong, giving to the casts the appearance of four sUts in 

 the beak, or of two slits and two oblique teeth," Mr. Salter thinks that this species, as 

 well as P. glohosus, may possibly belong to StricUandiriia. 



Position and Locality. Casts of this species occur abundantly in the Lower and Upper 

 Llandovery, but especially in the former. In the Loioer Llandovery at Quakers' Burial 

 Ground, and Guilsfield, Welshpool ; Pen-y-Craig ; Mathyrafal, south of Meifod ; 

 Llangynyw, Montgomeryshire ; Noeth Grug, Cefn Rhyddan, Cefn-y-Garreg, Llandovery ; 

 Builth, Rhyader, &c. ; Robeston Wathen and Haverfordwest, Pembrokeshire. In the 

 Upper Llandovery at Llwyn-y-Wormwood, Mandinam, and Peulan, Llandovery ; Builth, 

 Llangadoc ; Rosemarket, &c. ; Malverns, Church Stretton. Woolhope beds, Buildwas 

 (in ' Catalogue of Fossils, Museum of Pract. Geol.,' p. 52 (probably P. linguifer). 



In Ireland it occurs at Ballycar, Co. Clare (Mus. Geol. Survey, Ireland). 



I have not yet positively ascertained the existence of this species in Scotland, but 

 a search for it should be made in some of the Llandovery localities in the Girvau district, 

 Ayrshire. 



Pentamerus globosus, /. de C. Sow. (sp.)- PI- XIX, figs. 10 — 12. 



Atrypa globosa, J. de C. Sowerby. Sil. Syst., pi. xxii, fig. 2b, 1839. 



— — Phillips and Salter. Mem. Geol. Survey, vol. ii, part 1, p. 27", 



1848. 



Pentamerus globosus, Morris. Cat. Brit. Foss., p. 142, 1854. 



— — Salter. Siluria, 2nd edit., pi. viii, fig. 8, 1859. 



— — Id. Mem. Geol. Survey, vol. iii, pp. 276 and 360, 1866. 



Spec. Char. Circular, or shghtly transverse-oval; globose, or, when old, sub- 

 cuboidal, from the deflection of the front ; a very shallow undefined depression in the large 

 or ventral valve forming a shallow wave in the margin towards the opposite valve, 

 which is evenly convex, without a corresponding ridge ; lateral and frontal margins 

 rounded. In the cast of the ventral valve a long slit, extending to nearly half the length 

 of the valve, indicates the position of the vertical septum supporting the trough-shaped 

 chamber or converging dental plates. The surface of the cast is also irregularly marked 

 by obscure ridges. 



Length G, width 7 lines. 



Obs. I have never been able to procure the sight of more than a few internal casts 

 of the ventral valve of this species ; consequently, I can offer only a meager and incom- 

 ])lete description. The form of the shell is, however, so diff'erent from that of all the 

 other species of Pentamerus occurring in Great Britain, that, judging from these incom- 

 plete casts alone, it may be considered distinct. 



