The Invertebrate Fauna of the Uitenhage Series. 141 



similar in outline, but differs in having the urnbones more centrally 

 placed, and the posterior carinal ridge less prominently developed 

 and less steeply inclined. The posterior area is narrower, and 

 this and the carinal ridge have greater relative length than in 

 T. scliwarzi. In the African shell the urnbonal angle is sharper 

 and the umbonal region more prominently projecting. 



Tancrcdia brevis Lycett," from the Great Oolite, is also closely 

 similar in form, and may be distinguished principally by its slightly 

 greater convexity, its less prominently projecting umbonal region, 

 and its more pointed anterior outline. 



Again, the resemblance shown by T. sclucarzi to T. angnlata 

 Lycett,! from the Great Oolite, is very close, particularly in the 

 position of the unibones, the long antero-superior slope of the outline, 

 and the inclination of the carinal ridge ; in T. angulata, however, 

 the outline is rather more obtuse at the posterior angle, and the 

 aspect of posterior truncation is more marked, while the anterior 

 outline has a rather more pointed form. The resemblance of T. 

 schiuarzi to these Jurassic types is indeed so striking as necessarily 

 to arrest attention, and it is clear that such a form, if known before, 

 would have been seized upon by those who believed the Uitenhage 

 fauna to be of Oolitic age. How little reliance should be placed on 

 the evidence of a single occurrence such as this is well shown by a 

 study of the associated types, which can only be taken to indicate the 

 Lower Cretaceous age of this fauna. Although the genus Tancrcdia 

 reached its greatest development during Jurassic times, T. americana 

 Meek and Hayden I is known from Cretaceous strata on the Upper 

 Missouri and on Cache La Poudre River, in Colorado. The generic 

 position of T. americana has not been disputed, so far as I am aware, 

 but it is a much larger shell, not closely comparable with the one 

 we are discussing. 



A shell from the Upper Aptian of Spain, described by Coquand 

 as Tellina gibba, bears considerable resemblance to some forms of 

 Tancredia, and may very well be a representative of this genus, 

 though Stoliczka suggested that it belongs to Gray's Tellinella. 

 Coquand himself stated that it differs from other fossil Tellina by 

 its elongated form and particularly by the strong carinal ridge. 

 Speaking generally, this shell shares the main outward characters of 



* Morris and Lycett (1), part iii., p. 92, pi. xiii., fig. 8 (1855). 

 f Lycett (2), 341, pi. xiv., fig. 5 ; Morris and Lycett (1), part iii., p. 94, pi. xiii., 

 fig. 9 (1855). 



\ Meek (2), p. 142, pi. 38, fig. 1. 



Coquand (1), p. 101, pi. viii., figs. 9, 10. 



