Vol. 51.] FRESHWATER LAHELLIBRANCHIATA. 343 



casts in my monograph, because I had in my possession shells in a 

 better state of preservation. 



Locality. South Africa : Graaf Reinet. 



Pal^somutela ovata, Sharpe. 



1852. Iridina (?) ovata, Sharpe, Trans. Geol. Soc. ser. 2, vol. vii. p. 226, 

 pi. xxviii. figs. 3 and 4. 



These fossils, and especially that represented by fig. 4 (in Trans. 

 Geol. Soc), belong without doubt to the group of Palceomutda 

 Inostranzewi ; I came to that conclusion during my recent study 

 of the original specimen, and I am constrained to remark that the 

 drawings given by Sharpe are too much restored and therefore far 

 from being accurate. I find also that the specimen which served 

 as an original for Sharpe's description of the hinge-margin of 

 Iridina ovata belongs perhaps to another species (PI. XII. fig. 3). 



Locality- South Africa : Graaf Reinet. 



Forms of the Group Palceomutela Keyserlingi. 

 Pal^omtjtela, n. sp., aff. orthodonta, mihi. (PI. XII. fig. 5.) 



Compare 1892. Palceomutela orthodonta, Amalitsky, Palaeontographica, vol. xxxix. 

 p. 169, pi. xxi. figs. 18-23, 27, 28. 



The South African representative of this species differs from the 

 Russian forms by having somewhat more prominent umbones and 

 more anteriorly curved beaks. Although the one specimen examined 

 proves to be closely related to P. orthodonta, it is necessary, for the 

 want of further material, to consider it provisionally as a new 

 species. 



Dimensions 1 ', length 12, breadth 8, depth 6; average size of 

 Pussian forms : length 11|, breadth 7, depth 5. 



In Russia Palceomutela orthodonta is found in the Permian marls 

 and sandstones of the Oka- Volga basin at horizons A, B, C, and is 

 especially characteristic of horizon C. 



Locality. South Africa : Diamond mines at Kimberley. 



Pamiomutela trigonalis, mihi. (PI. XII. fig. 6.) 



1892. Palceomutela trigonalis, Amalitsky, Palajontographica, vol. xxxix. p. 170, 

 pi. xxi. figs. 15-17. 



This shell differs from the Pussian type, possessing somewhat 

 more prominent and more anteriorly curved umbones. Such 

 variations are frequent in the Russian examples of this species. 



Dimensions : length 13, breadth 9, depth 6. Russian forms are 

 very variable in size, the medium being : length 13, breadth 8, 

 depth 7. 



In Russia Palceomutela trigonalis is found on the upper horizons 

 A, B, and C of the Permian marls and sandstones of the Oka- Volga 

 basin. 



Locality. South Africa : Diamond mines at Kimberley. 



1 All measurements are in millimetres. 



