162 



BRITISH SILURIAN BRACHIOPODA. 



the beak is incurved; the area narrow, triangular, and divided in the middle by an 

 open fissure. Surface smooth, marked only with concentric lines of growth and 

 obscurely radiating fine longitudinal striae. Inside the ventral valve the two converging 

 dental plates are exceedingly small, supported by an equally small vertical septum. 

 In the dorsal valve there are in the middle of the narrow hinge-area two small converging, 

 but not united plates ; and close to the hinge are two small elongated scars, due to the 

 adductor or occlusor muscles. Two specimens measured — 



Length 2 inches 7 lines, width 2 inches 1 line, depth 10 lines. 

 „ 1 „ 9 „ „ 1 „ 7 „ „ 10 „ 

 Obs. In outline this species much resembles Pentamerus ohlongus ; but it is much 

 flatter and its beak not so much incurved; and its area and straight hinge-line also 

 distinguish it. Again, the external resemblance is in strong contrast with the interior ; 

 for St. lens possesses the small plates of Stricklandinia, and not the large ones of 

 Pentamerus ; I am therefore surprised that Prof. M'Coy should say, at p. 210 of his 

 'British Pal. Fossils,' that St. lens has exactly the same internal structure as P. ohlongus ; 

 and this remark inclines me to surmise that, while describing his so-termed P. lens, 

 he had before him a specimen or cast of P. ohlongus. ' Exteriorly, St. lens is at once 

 distinguished from St. lirata, both by its external and internal characters ; thus, there 

 are no cavities in the cast wherein a needle's point can be introduced, as in St. lirata ; 

 and, although at first sight there may not appear to be much difference in the respective 

 internal casts, this character will at once serve to distinguish them. Prof. M'Coy's 

 Pentamerus microcamerus is nothing more than a synonym of Stricklandinia lens, and, 

 as that author observes, is quite different from P. lavis, Sow., to which he supposed 

 Mr. J. de C. Sowerby had erroneously referred the fragment drawn in pi. xxi, fig. 12, 

 of the ' Silurian System.' In a foot-note to p. 229 of the second edition of Murchison's 

 'Siluria,' Mr. Salter observes that "the P. microcamerus (of M'Coy) appears not to be distinct 

 {xom. P. lens" and on a recent examination of the Silurian fossils in the Woodwardian 

 Museum at Cambridge, Mr. Salter and myself found an undoubted specimen of Strick- 

 landinia lens from the Lower Llandovery of Mandinam, labelled by M'Coy Pentamerus 

 microcamerus, and in another drawer, a specimen of St. lirata from May Hill, also labelled 

 by M'Coy P. microcamerus. This name, therefore, may be eliminated from our lists.^ 



Position aud Locality. Stricklandinia lens occurs in the Lower and Upper Llandovery 

 rocks, and is equally abundant in both. In the Lower Llandovery Mr. Salter has 

 identified it from Mandinam, Goleugoed, and Gorllwyn-fawr, in the Llandovery district ; 

 Priory Mill, Haverfordwest ; Cefn, near Buttington ; Mathyrafal, near Meifod ; Rhyader ; 

 and Pumpsant, Carmarthenshire. In the Upper Llandovery at Norbury, Bishops 



' I may here mention that, at Prof. Sedgwick's request, Mr. Salter has recently carefully re-examined 

 those Silurian fossils described by Prof. M'Coy which are in the Woodwardian Museum, Cambridge ; and 

 all the original labels have been preserved in those cases where the localities or names of the species have 

 undergone revision. The nomenclature of the beds is, of course, that of Prof. Sedgwick. 



