66 BRITISH SILURIAN BRACHIOPODA. 
more convex than the Lower Silurian form, D. od/ongata ; but this does not always hold 
good, for some Ayrshire examples of D. oblongata possess as much elevation as any of 
D. Morrisii I have yet seen. Never having obtained the lower or attached valve, I have 
transcribed the description given of it from a specimen in the Woodwardian Museum, 
by Prof. M‘Coy, in his ‘ British Pal. Fossils.’ 
Position and Locality. D. Morrisii occurs in the Wenlock shale and limestone of 
Dudley ; in the Aymestry limestone of Sedgley ; and in the Lower Ludlow of Leintwardine, 
Shropshire. 
DIscINA OBLONGATA, Portlock (sp.) Pl. VII, figs. 1—9. 
ORBICULA OBLONGATA, Portlock. Report Geology of Londonderry, &c., p, 445, 
pl. xxxii, fig. 13, 1843. 
—  t.avicata ? (Minster), Portlock. Ibid., p. 445, pl. xxxii, figs. 
W112. 
— SUB-ROTUNDA, Portlock. Ibid., pl. xxxii, fig. 10. 
- oBLONGATA, Jf‘Coy. Synopsis of the Silurian Fossils of Ireland, 
p. 24, 1846. 
Spec. Char. Nearly orbicular, or elongated oval. Upper or free valve moderately 
convex, conoidal, and more or less elevated, the incurved pointed vertex situated at a 
short distance from the posterior margin. Surface smooth, marked only here and there 
by a few lines of growth. Lower valve unknown. ‘I'wo specimens measured— 
Length 9, width 9, height 2 lines. 
SA Say Bane AOS erase Remi 
Ols. After an attentive examination of Portlock’s original examples of his O. /evigata 
Minster ?, O. oblongata, and O subrotunda, Portlock, I arrived at the conclusion that they 
were all slight modifications of a single species: all are derived from the same rock and 
locality, viz., Desertcreat, County Tyrone, Ireland. General Portlock thought he could 
identify, but with some uncertainty, one of his specimens with the Orédzcula levigata of 
Minster, ‘ Beitrage’ (“‘ Die Versteinerungen der Uebergangskalkes mit Clymenien und 
Orthoceratiten von Oberfranken”’), vol i, p. 80, tab. xiv, fig. 21, 1840. Minster 
describes his shell, which was small, as circular, highest towards the beak, which is only 
slightly arched, and at the outer margin depressed ; surface smooth, with hardly any lines 
of growth. His figure, however, does not leave in my mind acertainty that Portlock’s large 
example referred to O. /evigata belongs in reality to that species; and as it has not 
been possible for me to obtain a sight of the German type, I propose to make use 
of one of Portlock’s designations for the species under description. It may also be 
observed that in the same year in which Miinster gave the name of /evigafa to a German 
palzeozoic Discina, Deshayes applied the same designation to one of Leymeric’s French 
