The Invertebrate Fauna of tlic Uitenhage Series. Ill 



mens preserved in the collection of the Geological Society of 

 London are labelled " Sunday Eiver " (Atherstone and Bain), 

 "Prince Alfred's Eest " (Eubidge), and " Zwartkop Eiver" 

 (Eubidge). Specimens sent to me from the South African 

 Museum are from the Sunday's Eiver. Messrs. Eogers and 

 Schwarz record T. vau from the following localities : in the neigh- 

 bourhood of Uitenhage, ascending the Grass Eidge road, in the 

 uppermost of three beds of sandstone exposed in the dry water- 

 courses, and in the railway cutting between milestones 24^-24f on 

 the Graaff-Eeinet line; on Sunday's Eiver, in the upper beds exposed 

 in a white krantz on Wolve Kraal, on the north bank of the river. 

 In 1905 Mr. Eogers collected specimens 300 yards below Addo 

 Drift (Tunbridge's), left bank of Sunday's Eiver (40h, 41h, 42h). 

 An immature specimen (46h) from the same locality, may also 

 belong to Trigonia vau. 



Remarks. A large specimen of T. ran sent to me from the South 

 African Museum attains a height of 50 mm., measured from the 

 umbo. The ribbing of the flank ceases to be developed at a distance 

 of nearly 10 mm. from the inferior margin, in the neighbourhood 

 of which the shell surface is marked only by ridges and furrows of 

 growth. 



Sharpe gave a very accurate and characteristic figure of this 

 remarkable form, but the differences which distinguish T. vau from 

 T. stowi appear up to the present to have escaped observation, and 

 it is probable that the shells cited under the name T. vau by Stow" :: 

 are in reality to be ascribed to T. stowi sp. nov. I have had the 

 opportunity of examining and comparing a considerable number 

 of excellently preserved specimens of these two Triyonice, and find 

 that the characters which distinguish them from one another are 

 very constant. Several fully- grown shells of T. vau sent to me from 

 South Africa agree very perfectly with the original type and other 

 individuals in the collection of the Geological Society. The points 

 of distinction which may be readily observed in the adult shells of 

 T. vau and T. stowi are set forth in the remarks which follow the 

 description of the latter. During the youthful growth-stage, how- 

 ever, these two forms cannot be separated, so that it is uncertain 

 to which must be ascribed a young specimen obtained by Messrs. 

 Eogers and Schwarz at Walton's Farm, just below Dunbrodie on 

 the Sunday's Eiver (307), and another individual measuring 17 mm. 

 in length, collected between milestones 24i-24f on the Graaff-Eeinet 

 railway (309). There is the same doubt concerning an immature 



* Stow (1), pp. 199-505. 



