148 PERMIAN FOSSILS. 



length, and nearly five eighths in width : widest generally a little in front of its medio- 

 transverse line : somewhat obtusely rounded in front, and tapering behind : rather 

 compressed : posterior margins rounded : anterior margins sharp. Large valve 

 depressed in its anterior half, and slightly rounded posteriorly ; with a broad, some- 

 what flattened, shallow sinus in the medio-longitudinal region : umhone moderately 

 prominent and incurved : foramen moderate in size ; truncating the point of the umbone ; 

 and bounded inferiorly by the apex of the deltidium. Small valve obtusely ridged in 

 its medio-longitudinal region ; with the lateral surfaces sloping rapidly to the margins. 

 This is such a remarkably variable species, that it is difficult to draw up more than 

 an approximate diagnosis of it ; and for the same reason I have been compelled to 

 represent more specimens than would have been necessary under ordinary circum- 

 stances. Figures 30 to 43, inclusive, Plate VI, represent the principal varieties. 



Figs. 30, 32, and 37 (different specimens) are assumed to represent the typical or 

 normal forms. 



Figs. 31, 39 (one specimen), and 35 (young), a narrow variety. 

 Figs. 33, 36, and 43 (one specimen), a compressed wide variety, with a broad and 

 very shallow median sinus. Sp., Terebratulites latus, Schl. 

 Fig. 42, a variety, with a very deep median sinus. 



Fig. 34, a variety, with a narrow umbonal region, and a rounded anterior half. 

 Schlotheim considered some of the above varieties as species. I have no decided 

 objection to this view; but I feel myself utterly unable to separate one, form -from 

 another, they merge so imperceptibly into each other. It has therefore been deemed 

 the best plan to unite them under only one of Schlotheim's names, — the one generally 

 received. 



Terebratula plica, Kutorga, found in the Mountain Limestone of Sterlitamak is 

 considered by De Verneuil to be a variety of the present species : they undoubtedly 

 resemble each other in some respects ; but I have not yet seen any specimens of the 

 latter with the lateral marginal line so strongly curved as in the specimen represented 

 by Kutorga, in the 'Verb, der Min. gesellsch. St. Petersb.,' 1842, pi. v, fig. lie. The 

 specimen which I have partially represented in PI. VI, fig. 42, offers an approach to 

 it ; and Dr. Geinitz has figured a specimen offering a still nearer approximation 

 (Versteinerungen, pi. iv, fig. 27 c) : so that I am somewhat inclined to De Verneuil's 

 opinion. If Fischer's Terebratula Qualenii be correctly represented by Kutorga in the 

 work cited, I have considerable doubt of its being the same as Epithyris elongata, 

 having never seen any specimens so narrow in the umbonal region : there is an 

 approximation to it, however, in the specimen represented in PL VI, fig. 34. 



Some specimens appear to be identical with De Verneuil's Terebratula fusifortnis, a 

 Carboniferous species. Since my plates were engraved, I have procured specimens at 

 Tunstall Hill apparently undistinguishable from the one represented in the ' Geology of 

 Russia,' vol. ii, pi. ix, fig. 8 a, b. Specimens from the Carboniferous Limestone of 



