154 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [Feb. 6, 



AcT^ONiKA Sharpeana, spec. nov. 



" Cylindrites ?, undetermined." Sharpe, loc. cit. pi. 28. f. 24. 



Shell very minute, truncated, cylindrical ; spire depressed, obso- 

 lete; vertex large, flattened; last whorl with somewhat inflated 

 sides, base contracted, short ; aperture elongated, moderately ex- 

 panded towards the middle, subacute at the extremities. 



Loc. Associated with the above. 



AcT^ois'iJS'A Jenkinsiana, spec. nov. 



^^ ActcBonl, undetermined." Sharpe, loc. cit. pi. 28. fig. 25. 



Shell minute, elliptical ; apex acute ; spire of four whorls, elon- 

 gated, regularly conical ; aperture elongate, attenuated before and 

 behind. 



Loc. Lowest strata of the Zwartkop Crag, and Sunday's Eiver. 



Osteea^(Exogtea) JoifEsiAi^A, spcc. uov. PL YIII. figs. 3 a-3 c. 



Shell ovately orbicular, depressed, the larger valve only known, 

 with a large adhering surface, or simply attached by the small 

 involute umbo. Attached valve with a few strong and somewhat 

 rounded ribs, which indent the margin. 



Dimens. Length 1'57 mill., height 1-37. 



This species belongs to the section Exogyra, and but for that 

 might have been referred to Ostrea costata of the Lower Oolites of 

 Europe. 



Loc. Salt-pans of Bethelsdorp, with Cidaris Africana (Eu- 

 bidge). 



Osteea imbricata, Krauss, sp. 



The species Exogyra imhricata, Krauss, was referred by Sharpe to 

 the genus Gryphcea ; I have placed it in that of Ostrea, because 

 the numerous specimens in the Society's museum exhibit gradations 

 from one to the other of the so-called genera ; in fact this species 

 aifords a good illustration of the mere sectional value (which cannot 

 at all times be employed) of the groups Exogyra and Gryphcea. 



The gryphoid form of Ostrea imhricata is closely related to an 

 undescribed species of Gryphcea from the Oxford Clay of Weymouth. 



Loc. Sunday's and Zwartkop Eivers. 



PLACUIfOPSIS IMBRICATA, SpOC. UOV. PI. YIII. fig. 7. 



The unattached valve only is known ; it is thin, ovate, oblique, 

 and convex ; the apex is acute and marginal ; the dorsal margin of 

 the valve is straight ; the surface has concentric imbricating lamellae, 

 which towards the front of the valve occupy the ridges of the 

 smooth undulations. 



Dimens. Length 2-45 mill., height 1-64 miU. 



The general aspect of this, species is that of JPl. semistriata, 

 Bean, of the Cornbrash of Yorkshire; but the ornamentation of the 

 shell of that species is very distinct. 



Loc. In a brick -red shell-rock. One specimen from Prince Al- 

 fred's Eest (Eubidge). 



