130 PERMIAN FOSSILS. 



valve two thirds of its width in height ; rounded : umhone incurved : area nearly as high 

 as it is wide: fissure moderately large and open: median plate extending to nearly the 

 centre of the valve : dental plates rudimentary. Small valve moderately convex : median 

 rib broad, and evenly rounded. 



This species, which until now (January 1850) I have considered as inseparable 

 from Trigonotreta muUiplicata} has a striking resemblance to young specimens of the 

 Silurian Spirifer strigoplocm of De Verneuil (vide Geol. Russ., vol. ii, pi. iv, fig. 

 2 a, h, 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 Trigonotreta midtiplicata the present 

 shell differs in several important points : it is less in 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 Spirifer Blasii, a contemporaneous species, would 

 resemble the present fossil were it divested of the small ribs intervening the large ones. 



Trigonotreta Jonesiana occurs rather sparingly at Ryhope Field-House Farm, Dalton- 

 le-Dale, and Tunstall Hill in Shell-limestone. 



Trigonotreta alata, Schlotheim. Plate IX, figs. 4, 5, 6, 7, 8, 9, 10, 11, 12. 



Terebratulites alatus, Schl. Leonhard'sTaschenbuch, vol.vii, p. 58, pi. ii, figs. 9 a, 6 



(excluding figs. 1, 2, S^), 1813. 

 Petrefactenkunde, p. 250, 1820. 

 Boue, Edin. Phil. Journ., vol. xii, p. 144, 1825. 

 Brongniart, Tab. de Ter., p. 425, 1829. 

 Quenstedt, Wiegmann's Archiv., p. 79, 1835. 

 Geinitz, Gaea von Sachsen, p. 97, 1843. 

 Geinitz, Grundriss, p. 513, pi. xxii, figs. 1-4, 1846. 



— CONTOLUTUS, Phillips. King, Catalogue, p. 7, 1848. 



— UNDULATUS, /. de C. Sow. Geinitz, Versteinerungen, p. 13, pi. v, figs. 1-8, 



1848.3 



Terebratula alata 

 Spirifer alatus 



Diagnosis. — Somewhat fusiform : bi-areagerous : two inches and a half wide, arid 

 an inch long. Valves moderately convex : thick at their cardinal region : marked with 



^ 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, pi. ii : 

 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 palaeontologists 

 have also referred to it under the head of the next species, Trigonotreta undulatus. 



