342 PROF. W. AMALITSKY ON PERMIAN [Aug. 1 895, 



■wrinkled ; the anterior and posterior adductors are oval and large, 

 the former heing excavated posteriorly, and each surmounted by 

 small pedal muscular scars, the anterior one of which is separated 

 and situated under the hinge-line ; behind the anterior adductor- 

 scar is a supplementary small lunulate scar and a corresponding 

 muscular impression in tbe cavity of the umbo. Pallial scar entire. 



Horizon. Freshwater deposits of the Permian system of Russia 

 and of the Karoo Series of South Africa. 



The genus Palceomutela presents a very natural, group, the 

 numerous species of which are closely bound together by inter- 

 mediate forms, notwithstanding which it has been possible to 

 distinguish four groups among the Russian forms : 1, group of 

 P. Vernemli ; 2, group of P. Keyserlingi ; 3, group of P. Inostran- 

 zewi ; and 4, group of P. Murchisoni. All these four groups are 

 also found in the Karoo Series of South Africa. 



Their general characteristics are as follows : — • 



1. Group of Palceomutela Verneuili. Shell comparatively large, 

 transverse, elongate, oval, as a general rule flattened, with tumid 

 and slightly prominent umbones. 



2. Group of Palceomutela Inostranzewi. Shell as a general rule 

 smaller than that just mentioned, elongate, rhomboidal, rectangular, 

 triangular, oval, very convex, with prominent umbones ; a strong 

 ridge extends from the umbones diagonally across the shell to the 

 posterior inferior angle ; swollen in the direction from the umbones 

 backward towards the inferior angle, and compressed in the posterior 

 part. 



3. Group of Palceomutela Keyserlingi. Small shell, great variety 

 of shapes : elongate, rectangular, oval, trigonal, convex, with 

 moderately prominent umbones ; very tumid ridge, extending from 

 the umbones backwards to the inferior angle. 



4. Group of Palceomutela Murchisoni. Shell rhomboidal, of 

 various dimensions, with very prominent umbones ; ridge strong, 

 sometimes sharp, concave posteriorly, extending from the umbones 

 diagonally across the shell to the posterior inferior angle ; anterior 

 part swollen, posterior flattened. 



Forms of the Group Palceomutela Inostranzewi. 



Paeteomt/tela rhomboidalis, Sharpe (aff. P. Inostranzewi). (PI. XII. 

 figs. 1 and 2.) 



Compare Iridina (?) rhomboidalis, Sharpe, Trans. Geol. Soc. ser. 2, vol. vii. (1852) 

 p. 225, pi. xxviii. fig. 2. 



1892. Palceomutela Inostranzewi, Amalitsky, Palaeontographica, vol. xxxix. 

 pp. 172, 173, pi. xx. figs. 21, 22, 24^28. 



A broken piece of an interior cast (Bain Collection) with impres- 

 sion of the transversely striated hinge-margin, which is not quite 

 rightly reproduced by Sharpe (op. cit. fig. 2), belongs undoubtedly to 

 the group of Palceomutela Inostranzewi, and is quite identical with 

 the numerous casts of this group found at Nishny-Novgorod in the 

 reddish-brown sandstone of horizon B. I have not figured these 



