240 BRITISH SILURIAN BRACHIOPODA. 
the character of its ribs, which in Dalman’s species are fewer, straight, and simple. 
At p. 207 of the 2nd vol. of the ‘Geology of Russia,’ M. de Verneuil distinctly states, 
while describing O. calligramma— La surface des valves est ornée de plis simples et 
droits, qui, comptés avec soin sur plus de cinquante individus, nous ont offert tous les 
nombres depuis quinze jusqu’a quarante, mais se maintiennent le plus souvent entre 
vingt a vingt-cing. Ces plis, arrondis comme les sillions qui les séparent, naissent suc- 
cessivement le long du bord cardinal, et ne se réunissent pas tous au crochet. Dans les 
intervalles, on decouvre a la loupe, sur les échantillons d’une parfaite conversation deux a 
trois stries longitudinales extrémement fines.” I may also observe that the Lower 
Silurian shell attributed by Mr. Salter, with a point of doubt, to my O. Walsalhensis, 
belongs to another species. 
Besides the differences already recorded with reference to the shape and ribs in 
O. calligramma and O. rustica, | may mention that in Dalman’s shell the ventral valve 
is uniformly convex, and much more so than the dorsal, while in O. rustica the latter 
is usually the deepest and most convex; the ventral valve showing also a marked 
longitudinal depression from about the middle to the front. 
Having some years ago received, through the kindness of Prof. F. Schmidt, of St. 
Petersburg, a perfectly preserved example of Schrenk’s O. Osz/iensis, I was able to satisfy 
myself as to.its identity with Sowerby’s O. rustica. Therefore, in PI. XXXIV, 
figs. 13—17 represent Sowerby’s true O. rustica, figs. 18, 19 the var. rigida, and 
figs. 20—22 the var. Walsalliensis. 
Position and Locality. O. rustica appears to be a characteristic fossil of the Wenlock 
period ; is most abundant near Walsall, occurring also at Benthall Edge, Lincoln Hill; in 
Wenlock Shales opposite the ruins of Buildwas Abbey, near Wenlock, in Shropshire ; at 
Abberley and Callow Farm in the Abberley district; Dormington Wood, Woolhope 
district. 
No Scottish specimen has hitherto been discovered ; but in Ireland it occurs at 
Ferriter’s Cove, Dingle, County Kerry; and it is also mentioned by M‘Coy from 
Foylathurrig, in the same county. 
Abroad it occurs in the Island of Gothlaud, in Sweden, and at Erras, in Esthonia. 
_ ORTHIS CALLIGRAMMA, Dalman. Pl. XXXV, fig. 1—17; var. Davidsoni, figs. 18, 19; 
var. Scotica, figs. 20—22; var. virgata, figs. 23, 24.,and Pl. XX XVII, 
fig. 2. 
ORTHIS CALLIGRAMMA, Dal. Kon. Vet. Handl., p. 114, pl. ii, fig. 3, 1827. 
ORTHAMBONITES CRASSICOSTA, EMINENS, Pander. Beitr. zur Geogn. Russl., p. 81, 
pl. xxi, figs. 1, 2, 1830. 
ORTHIS CALLIGRAMMA, Hisinger. Letheea Suecica, p. 74, pl. xx, fig. 10, 1837. 
—  TRANSVERSA, SEMICIRCULARIS, TETRAGONA, ROTUNDATA, ROTUNDA, ZQUALIS, 
DATA, PLANA, Pander. Id., pl. xxii, figs. 1—8. 
