The Invertebrate Fauna of the Uitenhage Series. 89 



greenish-grey sandy marl, rather hard and very calcareous, near the 

 Bridge on the Zwartkop Eiver." 



Dimensions. (1) (2) (3) (4) 



Length 13 . 18 . 21 22mm. 



Height 9 . 12 14 . 13 



Depth of a single valve 4 . 6 ,, 



No. (2) is Tate's figured specimen. 



Remarks. This form is closely similar in general type to G. securis 

 (Leym.) * (Lower Cretaceous) and G. carinatus (Sow.) t (Gault and 

 Upper Greensand), and although I have been unable to ascertain 

 the characters of the hinge, the close agreement in form and orna- 

 mentation is perhaps sufficient justification for classing this shell in 

 the same generic group of the Arcidae. In the use of the name 

 Grammatodon I follow Mr. Woods. { 



Compared with G. securis, our shell is found to differ by the con- 

 siderably finer and more closely spaced ribs on the flank of the left 

 valve. With regard to the ribbing, there is greater similarity to 

 G. carinatus, but this, on the whole, is a decidedly more equilateral 

 shell, although specimens might be selected which in most respects 

 closely approach G. jonesi. G. carinatus frequently attains much 

 larger dimensions, with a proportionately coarser development of 

 the ornaments, than G. jonesi. A shell of similar type, and perhaps 

 related to G. jonesi, occurs in the Lower Neocomian beds of German 

 East Africa, which were correlated by G. Miiller with the Uitenhage 

 Series. Miiller described and figured this under the name Area 

 uitenhagensis,^ and drew attention to the apparent relationship to 

 Area jonesi Tate. A. uitenhagensis, which is associated with 

 Trigonia ventricosa (Krauss) and T. beyschlagi Miiller, differs from 

 Grammatodon jonesi by the fewer number and much greater breadth 

 of its ribs. 



GENUS UNIO A. J. Eetzius. 



UNTO UITENHAGENSIS Sp. nOV. 



Plate II., figs. 15, 15a. 



Description. The shell is of elongated oval outline, posteriorly 

 produced, and laterally compressed in the postero-inferior region of 



* Leymerie (2), p. 6, pi. vii., figs. 6, 7 ; Woods (3), vol. i., part 1, p. 44, pi. vii., 

 figs. 14, 15, pi. viii., figs. 1, 2 (1899). 



t J. Sowerby (1), vol. i., p. 96, Tab. 44, lower figure (1813) ; Woods (3), vol. i., 

 p. 45, pi. viii., figs. 3-8 (1899). J Woods (2). 



G. Miiller (1), p. 542, pi. xxv., fig. 5. [This name seems very unhappily 

 chosen.] 



