816 BRITISH SILURIAN BRACHIOPODA. 



tooth, or rather cardinal process, is bifid, and there is not that great difference in the 

 muscular impressions.) " I have little doubt" (continues M'Coy) "the shell figured by 

 Sowerby as the 0. anomala (Schloth.), ' Sil. Syst.,' pi. xxi, fig. 10 [see our PI. XLVI, 

 fig. 16], is a very old specimen of this species, elongated by compression, which has also 

 increased its convexity. Such specimens are not uncommon, indicating apparently the 

 thickening adult state, in which it often shows an approach to Strophomena grandis, when, 

 as sometimes happens, some of the strise in part of a specimen become more prominent 

 than the others." I consider, on the contrary, the difference between Stroph. convpressa 

 and St. grandis to be much greater than between it and St. expansa. Mr. Salter would 

 place that undeterminable specimen, named OrtJiis pseiido-peden by M'Coy, among the 

 synonyms of Strophomena compressa. This synonyma would, however, require much 

 consideration prior to being definitely accepted ; and I much regret that the material at 

 my command for examination, in connection with St. grandis, St. compressa, and St. 

 expansa, has not been greater. Good examples of all three should still be sought for and 

 carefully compared. 



Position and Locality. Stroph. compressa is stated to occur in the Caradoc and Upper 

 Llandovery formations, but especially in the latter. From the Caradoc : in Sandstone at 

 Horderly west, Bala Schists and Limestone of Craig-y-glyn, north of Rhaider, near 

 Llanarmonfach, east of the Berwyns ; Bala Schists of Moel Uchlas, Montgomeryshire, &c. 

 (M'Coy). 



In the Upper Llandovery at Presteign ; Marloes Bay ; Norbury, Chirbury ; Hope 

 Quarry, Minsterly, Damory Bridge, Tortworth ; May Hill. 



In Ireland, according to Prof. M'Coy, it occurs in the coarse Schists of Bardahassiagh, 

 Pomeroy, County Tyrone ; at Cappacorcogne Cong, County Galway ; and in several other 

 places ; but these require verification. 



Variety (!) — Llandeiloensis. PI. XLVI, figs. 11 — 14. 



This variety is of an elongated semicircular shape ; the hinge-line is quite as long as 

 the shell is wide, with sharply angular extremities. Ventral valve very slightly convex, 

 flattened at the ears ; area narrow ; fissure wide ; beak not projecting. Dorsal valve 

 slightly concave ; hinge-area linear. Surface of both valves covered with numerous, fine, 

 thread-like radii, a smaller and shorter one being interpolated between each two of the 

 principal ones. In the interior of the ventral valve the saucer-shaped muscular depres- 

 sion is very large, occupying fully a third of the inner surface of the valve, and is 

 separated along the middle into two lobes by a narrow median ridge, margined at its 

 posterior portion by two slender ridges (fig. 14). In the interior of the dorsal valve a 

 small bifid cardinal process is situated between two slender plates, on the outside of which 



