74. BRITISH SILURIAN BRACHIOPODA. 
ridges, with wider interspaces between them, the ridges not extending over the surface 
of the sulcus, which is smooth or very finely striated transversely. Proportions variable ; 
two specimens measured— 
Length 133, width 13 lines. 
St Cpe? elt ee Os 
Oés. It has been suggested by Prof. Morris that this shell might be the same as 
the Schizotreta elliptica of Kutorga;* and the same author further observed that it is 
probably the older form of Patella implicata, Sow. (‘ Sil. Syst.,’ t. xii, fig. 142), as well 
as identical with Patella antiquissima, Markl. (‘ His. Leth. Suec.’, t. xii, fig. 11). We 
must, however, at once dismiss the last two suppositions; for it will be seen, further on, 
that the so-termed Patella implicata, Sow., belongs to the genus Crania; and it is suffi- 
cient to glance at Hisinger’s figure of Patella antiquissima to feel satisfied that it is not 
the shell under description, and in all probability not even a Brachiopod. Some uncer- 
tainty, it is true, has been expressed as to whether Kutorga’s Schizotreta elliptica might not 
belong to the same species as my O. Fordesii ; and, unfortunately, I was unable to procure 
a sight of the Russian shell on which Kutorga founded his species. But, judging trom 
the figure, it would appear to be a much smaller shell than ours; and the apex of the free 
valve is much closer to the margin.” Prof. M‘Coy’s synonymy of his Oréiculoidea 
emplicata (Sow., sp. ?) is very defective; for he considers Kutorga’s Sch. elliptica as a 
synonym of Sowerby’s species, which, as we have already stated, is a Crania. I will, 
therefore, retain the specific designation of ‘* Horbesii”’ for our well-known British shell. 
Some adult examples of O. Fordesz are almost circular, with the free valve exceed- 
ingly convex, and the apex almost central. The groove in the opposite valve is of an 
elongated oval shape with an inner ridge, is nearly smooth, and up to .a certain age, no 
doubt, had a pedicle issuing from its small circular aperture; but this appears to have 
become cicatrized with age (?), for it cannot be observed in some very adult specimens. 
The first British figure of this interesting shell was published by myself in the ‘ Bulletin 
Soc. Géol. France ;’ and in the same year (1848) a very beautiful figure of the attached 
valve was published by Phillips and Salter in the ‘ Memoirs of the Geological Survey.’ 
Position and Locality. Orbiculoidea Forbes has been found in the Woolhope beds 
and Wenlock limestone and shales. It occurs in the Wenlock limestone of Dormington 
Wood, Woolhope ; at Winnal’s Farm, Malvern; at Marloes Bay (Mus. Geol. Survey) ; 
also in the Wenlock limestone near Dudley (British Museum). 
1 «Verhandlungen der Kaiserlichen Mineral. Gesellschaft fiir das Jahr,’ 1847, pl. vii, fig. 6. 
2 Orbicula elliptica, Kutorga, ‘ Dritter Beitrag zur Paleeontologie Russlands,’ p. 48, pl. vii, fig. 7, 1846, 
Silur. Kalkstein von Pulkowa; and Schizotreta elliptica, Kutorga, ‘ Verhandlungen Kais. Min. Gesell.,’ 
1847. Dr. Volborth informs me (21st of Feb., 1866) that the specimen of Schizotreta elliptica from 
Pulkowa, described and figured by M. Kutorga, appears to have been lost. During the lifetime of Dr. 
Kutorga, he had asked for the loan of it, but it could never be found ; and no specimens of the species seems — 
to occur in Russian collections. 
