46 Frederick Chcqntian : 



■Cythrropteron batesfokdiense, Chapman., var. aculeata, var. nov. 

 (Plate VIIL, Fig. 37). 



Description. — This variety is sufficiently well marked to merit 

 a distinctive name, since it has a more compressed carapace, and a 

 sharp ventral margin. Towards the posterior extremity, the ven- 

 tral border carries a series of short, strong prickles. The related 

 Eiuopean cainozoic form, C . triangulare sometimes shows very fine 

 . aculeations on the ventral edge. 



Occurrence. — Bore 11, 453-454 feet (Janjukian). 



Cytheropteron postumbonatum, sp. nov. (Plate VITI., Figs. 38), 



Description. — Carapace oblong, compressed at the extremities. 

 Seen from the side, the valveis tumid in the central area, depressed 

 around the margins; anterior extremity with a subangular margin, 

 posterior rounded; surface in anterior third swollen into a pear- 

 shaped inflation, behind which is a deep furrow joining the mar- 

 ginal depressed areas, whilst posteriorly the valve is again inflated, 

 and towards the ventral side this prominence is produced into a 

 short recurved hornlike process. Edge view subovate, compressed 

 at the ends, with the post-ventral process pointing outwards and 

 backwards. 



Surface of valve ornamented with numerous obscure pittings and 

 fine parallel striae towards the dorsal margin. 



Dimensions. — Length, .5 mm.; height, .21 mm.; thickness of 

 carapace, including the process, circ. .4 mm. 



Affinities. — ^The appearance in the Australian Cainozoic of this 

 modification of a well-defined Cretaceous group of Cytheroptera is 

 extremely interesting. C. postiimhonatuw is most closely allied to C. 

 umbo7iatvm, Williamson sp.,i a well-known member of the English 

 Chalk and Chalk-mai-1 of Norwich, Woolwich, Dover and Charing. 

 The Danish and British variety, C. umhonatum, var. acauthoptera, 

 Marsson var. 2 from the Island of Riigen, Norfolk, Dunstable and 

 Antrim, is distinguished from the specific form in having a much 

 longer postero-ventral spine and a prickly rather than a punctate 



1. Ci/theriira umbonata, William.son, Mem. Manch. Lit. and Phil. Soc, vol. viii., 1847, p. 79, pi. 

 iv., fig. 78. Cytheropteron umbonatwn, Will. ep. Jones, Mon. Cret. Entom. (Pal. Soc), 1890, p. 

 40, pi. i., fijrs. n-26. 



2. Cythere ac'tiithoptera, Marsson, Mittheil, naturw. Ver. Neu-Vorpomniern und Riigen, 1880, 

 p. 45, pi. iii., flifs. Ha-c. ('ytheropteron ui)ibonatn»i,\\\U. sp. var. acauthoptera, Marsson, var., 

 Jones, Mon. Cret. Entcm. (Pal. Soc), 1890, p. 41, pi. i., fljfs. 1113; pi. iv., figs. 22-29. 



