Vol. 51.] EEESHWATER LAMELLIBRANCHIATA. 345 



Forms of the Group Pal&omutela Verneuili. 



Pal^omutela semilunulata, mihi. (PI. XII. fig. 10.) 



1892. Palceomutela semilunulata, Amalitsky, Palseontographica, vol. xxxix. p. 166, 

 pi. xx. figs. 46-48. 



This is not a typical form of the group of Palceomutela Verneuili. 

 The South African representatives are quite identical with Russian 

 specimens. Palceomutela semilunulata is found in Russia on horizons 

 C and 1) of the Permian marls and sandstones of the Oka-Volga 

 basin. 



Dimensions : length 13, 15, 18 ; breadth 6, 7, 8£ ; depth 2|, 3, 3£ 

 (one valve). Russian forms : length 13-15 ; breadth 6-7 ; depth 

 2|-3 (one valve). 



Locality. South Africa: Graaf Reinet. 



Forms of the Group Palceomutela Murchisoni. 

 Pal^iomutela Murchisoni, mihi, var. (PI. XIII. fig. 1.) 



Palceomutela Murchisoni, Amalitsky, Palaeontographica, vol. xxxix. p. 177, 

 pi. xix. fig. 32. 



The African specimen of Palceomutela Murchisoni differs from 

 the Russian forms described by me in possessing a more obtusely 

 developed ridge, which extends from the umbones backwards to the 

 inferior-posterior angle. This distinction can only be of value when 

 a new variety is established, but at the same time it brings this 

 form into association with Palceomutela plana, which belongs also to 

 the group of P. Murchisoni. 



Dimensions : length 18, breadth 10 ; Russian forms : length 24, 

 breadth 13. 



In Russia Palceomutela Murchisoni is found on the upper horizon 

 B of the Permian marls and sandstones of the Oka-Volga basin, 

 near Nishny-Novgorod and Gorbatoff. 



Locality. Karoo Beds at Bedford, South Africa. 



Palceomutela plana, mihi. (PI. XIII. fig. 2.) 



1892. Palceomutela plana, Amalitsky, Palaeontographica, vol. xxxix. p. 177, 

 pi. xxii. fig. 45. 



The African form of this species differs from the Russian forms 

 only by its smaller size. 



Dimensions : length 15, breadth 9 ; Russian forms : length 24, 

 breadth 15. 



Palceomutela plana is found in Russia on the upper horizon B of 

 the Permian marls and sandstones of the Oka- Volga basin. 



Locality. South Africa : Graaf Reinet. 



Palceomutela, cf. l,evis, mihi. (PI. XIII. fig. 3.) 



1892. Palceomutela Icevis, Amalitsky, Palaeontographica, vol. xxxix. p. 177, pi. xx. 

 figs. 41-43. 



This badly-preserved but typical internal cast has a very great 



