130 PERMIAN FOSSILS. 
valve two thirds of its width in height ; rounded : wméone incurved : area nearly as high 
as it is wide: /isswre moderately large and open: median plate extending to nearly the 
centre of the valve: dental plates rudimentary. Small valve moderately convex : median 
rio broad, and evenly rounded. 
This species, which until now (January 1850) I have considered as inseparable 
from Zrigonotreta multiplicata,' has a striking resemblance to young specimens of the 
Silurian Spirifer strigoplocus of De Verneuil (vide Geol. Russ., vol. ii, pl. iv, fig. 
2 a, b,c, d), the most obvious difference between them being in the sharpness of the 
areal angle of the large valve, and in the umbone of the same valve projecting further 
behind the hinge-line, in the latter species. From Zrigonotreta multiplicata the present 
shell differs in several important points: it is less im width; has a more prominent 
umbone; a higher area; the ribs are more evenly rounded, and at a greater distance 
from each other; the median rib on the small valve is more evenly convex, or its 
corresponding furrow in the opposite valve more evenly concave; the dental plates 
also are smaller. De Verneuil’s Spzrifer Blasi, a contemporaneous species, would 
resemble the present fossil were it divested of the small ribs intervening the large ones. 
Trigonotreta Jonesvana occurs rather sparingly at Ryhope Field-House Farm, Dalton- 
le-Dale, and Tunstall Hill in Shell-limestone. 
TRIGONOTRETA ALATA, Schlothemm. Plate IX, figs. 4, 5, 6, 7, 8, 9, 10, 11, 12. 
TEREBRATULITES ALATUS, Schl. Leonhard’s Taschenbuch, vol. vii, p. 58, pl. ii, figs. 9 a, 6 
(excluding figs. 1, 2, 3”), 1813. 
= = »  Petrefactenkunde, p. 250, 1820. 
bass = »  Boué, Edin. Phil. Journ., vol. xii, p. 144, 1825. 
TEREBRATULA ALATA »  Brongniart, Tab. de Ter., p. 425, 1829. 
SPIRIFER ALATUS »  Quenstedt, Wiegmann’s Archiv., p. 79, 1835. 
a = »,  Geinitz, Geea von Sachsen, p. 97, 1843. 
= = »  Geinitz, Grundriss, p. 513, pl. xxii, figs. 1-4, 1846. 
— convoLutus, Phillips. King, Catalogue, p. 7, 1848. 
—  unpbuLatus, J. de C. Sow. Geinitz, Versteinerungen, p. 13, pl. v, figs. 1-8, 
1848.3 
Diagnosis.—Somewhat fusiform : bi-areagerous: two inches and a half wide, and 
an inch long. Valves moderately convex: thick at their cardinal region: marked with 
1 This is the reason why no more than one figure has been given of this species. Figure 19, Plate VIII, 
represents a young specimen twice the natural size. 
2 Schlotheim has represented different species under one specific name in the Taschenbuch, vol. vii, pl. 1: 
this has given rise to numerous errors: Von Buch correctly refers to fig. 9, but incorrectly to figs. 1 and 3: 
De Verneuil follows Von Buch; and Geinitz refers only to figs. 1, 2,3, none of which represents the present 
species. 
3 It. is probable that the names Spirifer trigonellus and S. paradoxus, given by several authors in their 
list of Permian fossils, have reference to this species: Von Buch and other German paleontologists 
have also referred to it under the head of the next species, Trzgonotreta undulatus. 
