Vol.51.] FEESHWATEB LAMELLIBEANCHIATA. 341 



sculpturing, that they belong to the group of Palceomutela Keyser- 

 lingi and to the species : P., n. sp. aff. orthodonta, mihi, P. trigo- 

 naliS) mihi, P., n. sp. aff. Golowkinskiana. This group is found on 

 the horizons, A, B, C, of the Upper Permian marls and sandstones 

 of the Oka- Volga basin. 



3. Prof. T. Rupert Jones has shown me a piece of greenish-grey 

 shale containing numerous shells described by him as Iridina 

 (?) oblonga 1 which was brought by Prof. Henry Drummond from 

 Maramura near Lake Nyassa, Central Africa, and is now in the 

 British Museum (Natural History). Prof. Rupert Jones considers 

 these fossils similar to Iridina (?) described "by Sharpe from Graaf 

 Reinet in South Africa. They are badly preserved, exhibiting only 

 internal casts, thus preventing a more definite determination, but 

 probably we have here also forms representing the groups Paloeo- 

 mutela Inostranzewi and Palceanodonta (Naiadite-s) Fischeri, found 

 on the upper horizons of the Permian marls and sandstones of the 

 Oka- Volga basin. 



4. Mr. P. Bullen Newton has been kind enough to show me the 

 David Fraser Collection preserved in the Geological Department of the 

 British Museum of Natural History. Among numerous lamellibran- 

 chiata from the Karoo Series (Beaufort Beds) I was enabled to 

 determine a well-preserved specimen as Palceomutela Murchisoni, 

 mihi var. (loc. Bedford, South Africa), so very characteristic of the 

 upper horizons of the Permian marls and sandstones near Nishny- 

 Novgorod and Gorbatoff. 



From the foregoing remarks it will be seen that those forms 

 which could be defined are from the Beaufort Beds — partly from 

 the upper (Graaf Beinet, Bedford) and partly from the lower 

 (Kimberley) horizons ; and they belong to the genera Palceomutela, 

 mihi, a»d Palceanodonta, mihi, which I consider referable to the 

 family Anthracosidae. 



Antheacosid^e (Pal^otjnionid^:), mihi. 



Palceomutela, mihi. 



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

 1886. Anthracosia, Amalitsky (pars), ' Ueber das Alter d. Stufe d. Bunten 

 Mergeln im Bassin d. Oka und Volga.' 



1889. Anthracosia, Krotow (pars), Mem. Com. Geol. de la Russie, vol. vi. 

 pp. 491, 511. 



1890. Iridina (?), T. Rupert Jones, Geol. Mag. 1890, pp. 409, 553-558. 

 1892. Palceomutela, Amalitsky, Pala^ontographica, vol. xxxix. pp. 159-160. 



Generic diagnosis. Shell equivalve, inequilateral, elongated, 

 rhomboidal, trapezoidal, ovate, triangular. Ligament external. 

 Hinge-margin curved, angulated, or straight, thickened below and 

 behind umbones, covered with numerous irregular, transverse or 

 oblique, small striae situated on both sides of the umbo, or more 

 rarely behind the umbo only. Muscular scars 6 ; adductors and 

 pedal (retractor) muscles strong, sometimes transversely jagged or 



1 Geol. Mag. 1890, p. 557. 



