Cretaceous Gastropoda, and Pelecypoda from Zululand. 83 
GONIOMYA Sp. 2. 
Plate VI., figs. 20, 21. 
Observations. — This form of Goniomya has normal-sized valves 
standing open from the umbones and chiefly exhibiting posterior 
characters, the ventral and the major part of the anterior regions 
not being preserved. Although mostly a cast, fragmentary remains 
of a delicate thin shell are occasionally apparent, and as they do not 
show structure it is possible they are mere films which do not 
represent the actual outer surface of the shell. The valves are only 
moderately convex having strongly incurved, small, depressed and 
contiguous umbones, on each side of which an oblique ridge is 
present which in the posterior direction is very obtuse and circum- 
scribes an elongate and slightly excavated escutcheon area, having in 
the centre a narrow cavity which probably held the ligament. On 
account of the valves being open a considerable divergence from the 
umbones is observable in the small part of the anterior region still 
preserved, and beneath the umbonal ridges, which in this case are 
sharply defined, runs a smooth internal sulcation. Compared with 
other specimens of this genus, the posterior region is rather short 
and rouuded at the margin, the whole contour having been probably 
more or less cylindrical, moreover the original height might very 
well have measured 25 mm., whilst the actual posterior length of 
the specimen from the apices of the angulated ribs is 18 mm. 
The sculpture consists at the umbones of numerous lateral, straight, 
divergent costse united in the ventral direction by horizontal costae, 
these latter being afterwards replaced by the ordinary deep V-shaped 
angulations characteristic of the genus, the apices being in regular 
vertical arrangement from their commencement. The dorsal ends 
of the lateral costae curve upwards at the margin, whilst in the 
postero-ventral direction these ribs become gradually wider and 
necessarily fewer in number. 
From what can be seen of the contour lines, this specimen is 
likely to have been a more cylindrical form than that represented by 
Goniomya sp. 1, although its fragmentary nature increases the diffi- 
culty of a true comparison. The shortness of the valves posteriorly 
curiously resembles Jurassic forms such as G. proboscidea of Agassiz, 
from Switzerland, but the sculpture of that species is probably less 
vertically arranged from the umbones and the later postero-lateral 
costse are rather finer and more numerous. 
Locality. — Tributaries of the Manuan Creek. 
