The Invertebrate Fauna of the Uitenhage Series. 153 



Meretrix labadyei (d'Archiac),* from the Tourtia of Tournay, has 

 an almost identical outline, but its valves are much more convex. 

 The same character distinguishes several other Cretaceous forms 

 ascribed to Cytherea or Venus, which, when compared with our shell, 

 are seen to have a very similar outline. 



In the shape of the shell, the inconspicuous umbones, and the 

 compressed form, resemblance is shown to Tapes picteti de Loriol,t 

 from the Gault of Cosne (Nievre), which, however, is not so elongated 

 relatively to height, and moreover, has a coarser concentric orna- 

 mentation. A similar resemblance is shown to Tapes patagonica 

 Stanton,J from the Belgrano beds (Lower Cretaceous) of Patagonia, 

 but the points of distinction are plainly seen in the less elongated 

 figure, the greater inflation, and the coarser concentric ornamenta- 

 tion of the Patagonian shell. 



A shell from supposed Lower Cretaceous strata in the Cameroons 

 (left bank of Mungo Eiver), described by von Koenen as Cytherea 

 wohltmanni, differs from Meretrix uitenhayensis in the greater 

 inflation, the more inequilateral form, and the prominence of the 

 umbonal region. 



A word may be added regarding the generic position of this form. 

 In no specimen has the interior been seen, so that a precise generic 

 determination cannot really be made with certainty ; but a com- 

 parison with other species in which the hinge-teeth are known, 

 justifies a provisional reference to Meretrix, if this name be applied 

 in the broad sense in which the name Cytherea has for long been 

 used, with reference to Cretaceous forms. The tendency of modern 

 work is to set closer and closer limits to the application of long- 

 established generic names amongst lamellibranchs, as in other 

 classes of Mollusca. It is highly probable, when evidence of 

 internal characters can be obtained, that an extension of this 

 principle to Cretaceous forms, on the lines carried out in the classifi- 

 cation of recent and Tertiary species, may eventually show the in- 

 applicability of the name Meretrix (equivalent to Cytherea as 

 commonly used) to such a form as the one here described. From 

 practical considerations, however, it will often be necessary, as in 

 the present case, to continue to utilise in a broad sense a name 

 which, though perhaps technically wrong, conveys as definite a 

 meaning as the available evidence for the time being allows. 



* d'Archiac (1), p. 303, pi. xiv., fig. 7. t ^ e Loriol (4), p. 64, pi. vii., fig. 21. 



I Stanton (3), p. 23, pi. iv., figs. 12, 13. 



von Koenen (1), p. 36, Taf. iv., tigs. 6, 8, 9 ; since shown to be of Upper 

 Cretaceous age, see Solger (1). 



