36 
DEVONIAN PAUNA. 
with Goldfuss's figured specimens, the differences are such as may be accounted 
for by its being a larger and more aged example. Our shell is proportionately 
longer, its umbo is more prominent, and its anterior side more receding. The 
hinge teeth are not very clearly seen, but on the whole they seem very similar to 
those in Goldfuss's fig. 9/. Goldfuss figures several specimens of different sizes, 
and it is to be observed that as their size increases their shapes approximate to 
ours, which is about half as long again as the largest of them. 
Affinities. — From Mecijnodon colmnbinus this shell is distinguished by several 
characters noticed under that heading, and is, I tbink, certainly distinct from 
that species. 
2. Oedee.— ASIPHONIDA, Fleming, 1828. 
1. SuB-OEDEE.— HOMOMYARIA, Zittel, 1881. 
I. Family. — Teigoniid2E, Fleming, 1828. 
1. Genus. — Protosohizodus, de Eoninclc, 1885. 
Under this heading de Koninck has separated the Carboniferous species of 
ScMzodus on account of a difference in the dentition. It is more probable that a 
Devonian shell, known only by its external features, would agree with these 
rather than with the more recent forms of ScMzodus proper. 
1. PeOTOSCHIZODUS (?) TEIGONBLLUS, n. sp. PI. Ill, fig. 2. 
Description. — Right valve large, flat, ovoid, transverse. Umbo small, acute, 
anterior, oblique, subproximate, hardly incurved. Anterior margin broad, 
concave under the umbo, and then convex. Inferior margin slightly convex. 
Infero-posterior corner very convex. Posterior margin oblique. Contour of shell 
slightly and uniformly convex on the back, rapidly rounded on the anterior and 
posterior sides. Surface ornamented by close, regular, microscopic strias. 
Shell-structure thin. 
8ize of valve. — Length 28 mm., breadth 22 mm., depth 7 mm. 
Locality. — A single specimen from Lummaton is in my Collection. 
Remarks. — This is a veiy perplexing shell, as the critical parts are obscured 
or broken away. Mr. Etheridge and I came to the conclusion that it most 
