188 
Spirifeva convoluta, T. Davidson, 1859, Mon. Brit. Carb. Bracli., p. 35, pi. 5, fig. 9-15 
(fig. 12 exclnsis) and pi. 50, fig. 1, 2. 
,, GOnvolutci ? K. Etheridge, Senior, 1872, Quart. Jourii. Gleol. Soc., XXVIII, p. 
335, pi. 17, fig. 3. 
This is a fusiform shell, three or four times as hroad as long. Its 
hinge area is very long, with suh-parallel margins, and occupies the entire 
length of the shell ; its deltoid fissure is rather hroad and partly recovered hy 
a pseudo-deltidium. The ventral valve is a little deeper and more ventricose 
than the dorsal valve ; its heat, thick and much recurved, hides part of the 
deltoid fissure ; the ventral furrow varies very much in In’cadth and depth, hut 
corresj)onds to the sometimes much-elevated dorsal ridge. Both the dorsal ridge 
and the ventral furrow are ornamented with five or six longitudinal folds, rather 
less distinct than those on the rest of the surface. The lateral folds, sixteen or 
twenty on each side, are oblique, often bifurcated, and scarcely visible towards 
the lateral margins. The internal casts are very remarkable, and without the 
external impressions (which have enabled me to determine the species Avith 
certainty) it would have been difficult to refer the specimen to its species. 
This impression, from which I have taken my figure (PI. XII, Pig. 2), leaves 
me in no doubt as to its origin; it has evidently been produced by a shell of large 
size, which, in disappearing, has left in the rock all the details of its ornamenta- 
tion. The internal casts compared with the external impression show that the 
shell is rather thick, and the muscular impressions are strong and deeply 
hollowed into the shell. On each side of these impressions the internal 
surface shows a number of small irregularly-arranged pits, which are repro- 
duced in relief on the mould ; these are generally less pronounced on the 
dorsal valve, and many specimens are deprived of them. 
Dimensions . — The dimensions of this species are very variable. The 
largest specimen is about fifteen centimetres broad, and four centimetres long. 
Horizon and Localities . — Professor Phillips, who first described this 
species, found it in the Upper Limestone at Bolland. I have found it in 
limestone of the same age at Vise. M. E. Dupont found it in the Middle 
Limestone at Pauquys, where it is rather abundant. Por some time the casts, 
found in the Carboniferous beds of Tasmania and Australia, were called 
S. avicula, and were described under that name hy Messrs. Sowerhy and 
Morris. The Ptev. W. B. Clarke has sent me a large number from Muree 
Quarry, Paissell’s Shaft, Anvil Creek, S. Ileliers, Mount Wingen, jEllalong, 
