38 
Transactions of the Boyal Society of South Africa. 
extending from the umbonal region and terminating in a marginal 
notch. Internally the valve is seen to be well excavated ; it pre- 
sents a wide and sub-arcuate hinge region with the divergent liga- 
mental furrows, whilst some of the lateral and central teeth are 
well preserved ; the marginal denticulations are also seen in places. 
Named after the late C. L. Griesbach, Esq., formerly Director of 
the Geological Survey of India, and author of an important memoir 
{Quart. Journ. Geol. Soc. for 1871) on the geology and palaeontology 
of the south-eastern territory of Africa, known in the present day as 
Pondoland. 
Locality. — Tributaries of the Manuan Creek, and north end of 
False Bay ( = the figured examples). 
Family TKIGONIID^. 
Genus TEIGONIA, Bruguiere, 1789. 
Encyclopedie Methodique [Paris], 1789, vol. i., p. xiv. 
Tkigonia cricki, sp. nov. 
Plate v., figs. 10-15. 
Descri])tion. — Shell of crescentic form with moderately inflated 
sides, surface depressed at front end ; postero-marginal area deeply 
concave, smooth, rounded, medianly furrowed, tapering from the 
umbo to a basal width of 10 mm. in the larger specimen and covered 
with fine and closely arranged concentric striations ; escutcheon 
wide, concave, lengthy, rounded beneath the umbones, inner 
margins raised, surface showing obscure transverse costellse ; valves 
ornamented with prominent, elevated, rounded, oblique costae, com- 
posed of regular smooth ring-like contiguous segments which are 
largest anteriorly, the costse gradually diminishing to a thin attenuated 
end and joining the posterior margin in an upward oblique direction ; 
costae divided by wide and deep grooves bearing growth striations ; 
umbo incurved, of moderate inflation and furnished with several 
rounded costae (ten can be counted in a distance of 10 mm. from 
the apex). 
Di7nensio7is. — 
Specimen with closed valves — 
Maximum diameter 27 mm. 
Width of escutcheon area 15 ,, 
Left valve of the largest specimen — 
Width (maximum) 23 ,, 
Height from umbonal region to postero- 
ventral end 43 ,, 
