154 Annals of the South African Museum. 



GENUS PSAMMOBIA Lamarck. 



PSAMMOBIA ATHEBSTONI Sharpe. 



1856. Psammobia atherstoni D. Sharpe, Trans. Geol. Soc. Lond., 

 ser. 2, vol. vii., p. 196, pi. xxii., fig. 11. 



This was found in the cliff below the old school-house at Dun- 

 brodie, on the right bank of Sunday's Eiver (321, 325). A specimen 

 from this locality, submitted to me, agrees very closely with the 

 largest individual figured by Sharpe. The Dunbrodie specimen 

 measures 25 mm. in length and 15 mm. in height ; it is a left valve, 

 having the characteristic compressed form and flattened flank and 

 very inconspicuous umbo. Sharpe records this shell from the 

 " Sunday Eiver near Enon, in a grit sometimes full of the casts of 

 the shell." At Dunbrodie Psammobia atherstoni is associated with 

 ActcBonina atherstoni, Turbo atherstoni, Pecten cottaldinus, and other 

 forms. Messrs. Eogers and Schwarz mentioned the occurrence of 

 Psammobia atherstoni in the Wood Bed series of the Bezuidenhout's 

 Eiver below Blue Cliff,* but this name was probably applied to 

 specimens which I have referred to the genus Unio. 



The generic determination of this species must be regarded as 

 provisional. No specimens showing satisfactorily the internal 

 characters have been available for study, and true relationship with 

 Psammobia (or Gari Schumacher, if this be regarded to have 

 synonymic value) still remains to be proved. The propriety of 

 considering the name Gari to possess the same significance as that 

 which has been ascribed to Psammobia (sensu lato) is perhaps still 

 open to question. The shells we are dealing with in the present 

 instance are smooth and without radial markings, and this fact, 

 together with the slight doubt concerning even the broader generic 

 relationships, seems to justify the retention, for the time being, of 

 Lamarck's more familiar and more widely accepted name. It 

 appears reasonable, under the circumstances, to use as a provisional 

 measure a nomenclature which clearly indicates the supposed rela- 

 tionships, though it may perhaps be technically erroneous. To 

 hazard a "correction" of nomenclature on an insecure basis of 

 imperfect knowledge is a step for which it would probably be more 

 difficult to find justification. 



* Kogers and Schwarz (1), p. 13. 



