254 CATALOGUE OF THE FOSSILS OF THE PERMIAN SYSTEM 
31. SPIRIFER, Sowerby. 
1. S. unpuLAtus, Sow. 
Spirifer undulatus, Sow., Min. Conch., tab. 562, f. 1 ; Gen. 
Shells, Spir., f 3. 
Terebratulites alatus, Schloth. Min. Taschb. vii., pl. 2, f. 1, 
3, 6. 
In Magnesian-limestone ; not common. Tynemouth Cliff, 
Humbleton, Tunstall, Thickley. 
This fine Spirifer varies considerably in appearance, some in- 
dividuals being almost semicircular, and others subtrigonal and 
very much winged. On the casts the apical recesses of the lower 
valve are very granulous. ‘The spiral coil is large and nearly 
fills the cavity of the shell, and is finely preserved in specimens 
found at Humbleton. The quarrymen term this shell the 
“ butterflee.” 
2. S. oristatus, Schloth. 
Terebratulites cristatus, Schloth., Min. Ak. vi., pl. 1, f. 3. 
In Magnesian-limestone; notcommon. Tunstall, Humbleton. 
The general form of this shell is semicircular. The lower 
valve is rather deep, and almost divided into two parts by a 
large mesial plate which extends from the beak nearly to the 
centre of the valve. The upper valve is slightly convex. The 
outer surface of both valves is folded into nine or more sharply 
angulated plaits, and covered all over with minute elevated gra- 
nulations. Internally the shell is minutely punctured. The 
lines of growth are generally very distinct. It may be ques- 
tioned whether this species is identical with the S. octoplicatus, 
Sow. In the latter the general form is more tumid and the 
beaks are more recurved than in the former species. 
3. S. muLtrpTicatus, Sow. 
Spirifer multiplicatus, Sow., Geol. Tr. 2nd ser. iii., p. 119. 
In Magnesian-limestone ; not rare. Humbleton, Silksworth, 
Dalton, Tunstall. 
This species is more common than either of the former, and 
owing to the manner in which it is preserved it is by far the 
most interesting. It often occurs in a soft powdery substance, 
