232 BRITISH SILURIAN BRACHIOPODA. 
there is no essential difference. Mr. Salter also has authorised me to state that O. vaticina 
was the name he gave to the shell before he found that O. denticularis was nothing 
else. 
On the 3rd of January, 1867, Mr. Plant enclosed me a natural-sized photograph of a 
large specimen (Pl. XXXIII, fig. 27), which he had procured from near the top of 
Murchison’s ‘ Lingula-flags,’ at Rhiw Felyn, in North Wales, and which he considered to 
be distinct from O. denticularis ; and in this opinion at one time I felt almost disposed to 
concur; but since then the discovery of several intermediate-sized examples by Mr. 
Homfray at Ogof-ddu, Criccieth, near Portmadoc, and by Mr. Belt at Penmain Pool, 
west of Dolgelly, has induced me to look upon the larger and smaller specimens as 
mere modifications of form, age, and state of fossilization of a single species; the 
shell found by Mr. Plant being likewise flattened out and distorted by pressure. It is 
quite possible, as was stated to Dr. Lindstrém by Prof. Angelin, that several species may 
have been confounded with Wahlenberg and Dalman’s unfigured Azomites lenticularis ; 
but there appears to be much probability that Mr. Salter is correct in his identification of 
our English specimens with those found in Sweden. 
Position and Localily. Orthis lenticularis seems to be confined to the Upper Lingula- 
flags (Dolgelly groups of Belt, or upper portion of the Ffestiniog group of Sedgwick), 
and occurs at Penmorfa Church, near Tremadoc; near Criccieth, at Ogof-ddu Cliff, 
Gwerny-y-Barcud, Rhiwfelyn, and in several other Welsh localities. 
The foreign localities have already been mentioned. Baron von Buch observes that 
the individuals of this species are assembled by millions, without shell, piled one upon 
another over a great thickness of strata (just as we find them to occur in North Wales), 
and of themselves compose the aluminiferous schists of Andrarum in Scania. Dalman 
mentions that these beds extend over all West Gothland, and over certain other provinces 
of Sweden, which he does not name. It occurs also in Norway. 
Ortuis auata, J. de C. Sow. (sp.). Pl. XX XIII, figs. 17—21. 
Sprrirer ? auatus, J.de C. Sow. Silurian System, pl. xxii, fig. 7, 1839. 
Ortuis autata, Salter. Siluria, 2nd ed., p. 55, fig. 15; and pl. v, fig. 6, 1849. 
— —? Id. Memoirs of the Geol. Survey, vol. iil, p. 337, 1866. 
Spec. Char. Semicircular, with expanded angular extremitics, wider than long, 
slightly indented in front; hinge-line straight, and as long as the greatest breadth of shell. 
Dorsal valve very slightly convex, flattened laterally near the cardinal line and extremities ; 
a longitudinal depression, commencing likewise at the centre of the umbone, gradually 
deepens and widens as it nears the front ; hinge-area very narrow. Ventral valve mode- 
rately convex, and flattened near the cardinal extremities; area narrow, fissure small. 
