NEWTON: ALECTRYONIA UNGULATA IN S.E. AFRICA. 139 
REMARKS. 
According to the age of this species so it varies somewhat 
in the characters here given, though the smooth median groove 
can be always traced. In general contour and in possessing 
the prominent lateral plications, it resembles other forms of the 
genus, such as A. frons, Parkinson, sp., 4. carinata, Lamarck, 
sp., 4. macroptera, J. de C. Sowerby, etc.; but in all these 
shells the lateral plications meet on the dorsal summit of the 
valves, and exhibit no indication of the channel or groove, which 
is the distinguishing character of 4. uagulata. 
The present specimen from Sofala is fragmentary (its termi- 
nation being wanting) and waterworn, though the distinctive 
features are well represented. Its valves are attached, the 
buccal view showing the powerful interlocking nature of the 
dentiform processes. 
Although this species has the widest geographical distribu- 
tion of any of the Ostreidze it is geologically restricted to the 
uppermost cretaceous deposits known in South Africa as the 
zone of Puzosia Gardeni, and in Europe as the Campanien and 
the Meestrichtien, the former being the highest division of the 
Senonian formation, the latter the lower portion of the Danien. 
In England this upper Cretaceous zone is represented by the 
topmost beds of the Upper Chalk developed at Mundesley and 
Trimmingham in Norfolk, where the species has been recognised 
as alaeformis and canaliculata, which together with falcata, 
Junata, and /arva of other countries represent the junior stages 
in the growth of the true wngulata. — 
From the highest cretaceous strata of Southern India, 
called the Ariyalur Group, this species was recorded by Forbes, 
nearly half a century ago, under the name of Ostvea tegulanea ; 
more recently in 1889* it was discovered in large numbers in 
Madagascar, and now that it is found in S.E. Africa we are 
furnished with additional evidence in favour of the view that 
*R, B, Newton, Quart. Journ. Geol, Soc., 1889, vol. xlv., pl. 14, fig. 12, p. 333, 
