132 PERMIAN FOSSILS. 
SPIRIFER UNDULATUS, J. de C. Sow. Phillips, Encye. Met., vol. iv, p. 617, 1834. 
— — Von Buch, Ueber Delthyris, p. 37, 1834. 
be) 
mee — ae Thomson, Outlines of Geology, &c., vol. ii, p. 326, 
1836. 
TEREBRATULA UNDULATA ,, Deshayes, Lamarck’s Animaux sans Vertebres, 
2d ed., vol. vu, p. 371, 1836. 
SPIRIFER UNDULATUS A Le Cocq., Transl. of Von Buch, Mém. Soc. Geol. 
de France, t. iv, p. 183, pl. vii, fig. 6. 
_ — o Morris, Catalogue, p. 131, 1843. 
— — a Brown, Fossil Conchology, p. 110, pl. 50, figs. 
27, 28, 1843. 
— — 53 Lyell, Elements of Geology, p. 416, fig. 241, 1838. 
— — De Verneuil, Bull, Soc. Géol. de France, 2° série, 
vol.i, p. 28, 1844. 
—— — We Geol. Russ. vol. 1, p. 222, 1845. 
(?) —  HyYsTERICUS (7) ,, Idem, vol. ii, p. 173, pl. vi, fig. 12, 1845. 
(?) —  (EspEcE INDETERMINEE), De Vern. Loc. cit., fig. 13. 
—  unpuxatus, J. de C. Sow. Tennant, Strat. List., p. 89, 1847. 
— axatus, Schl. King, Catalogue, p. 7, 1848. 
—  uNnpuLAtus, J. de C. Sow. Howse, Trans. T. N. F. C., vol. i, p. 254, 1848. 
Diagnosis.—“Transversely elongated, very convex, with pointed extremities, radiated 
transversely, and deeply striated ; front elevated, with a rounded sinus; radii obtuse, 
about 16 on each side the central elevation; beaks a little removed; area flat, 
narrow. (J. de C. Sow.)! 
This species has often been confounded with Zrigonotreta alata, both of which 
simulate each other; but 7. undulata differs from 7. alata in being more tumid at 
the umbones, more produced in front, and a narrower shell: the last difference is 
well displayed in young specimens of both species, as represented in figs. 10 and 16, 
Pl. IX.’ Both species agree in other respects. 
Mr. J. de C. Sowerby having kindly favoured me with an exammation of the 
original specimen of this species, figured in the ‘ Mineral Conchology,’ I embrace the 
present opportunity of drawing up from the same the following description, which, 
with Mr. Sowerby’s diagnosis, and the figures herein given (vide Pl. IX, figs. 1, 2, 3), 
will enable the reader to form a tolerably correct idea of its characters. Semi- 
elliptical in marginal outline: bi-areagerous: very mequivalved : two inches in width, 
and an inch and an eighth in length, that is, from the umbone to the termination of the 
sius-prolongation in the large valve. Large valve moderately convex: median sinus 
broad; rather deep; with a faint median rib: Jateral surfaces each with fourteen or 
more cord-like ribs, about half of which have resulted from dichotomy on the umbonal 
region: wmbone much incurved, and projecting considerably behind the hinge line : 
! Mineral Conchology, vol. vi, p. 119. 
? Since the plates were engraved, I have collected young specimens half the size of those in the figures 
referred to, showing the same differences. 
