228 
which to describe his new species, and the figure given is a 
rather faulty representation of his type. Material obtained 
since furnishes the following information, and establishes it 
as a true species. 
The dimensions given are:—Antero-posterior, 20 mm. ; 
umbo-ventral, 18; sectional diameter, 10°5. My largest ex- 
ample measures 36 by 37 by 19°5. As it grows it therefore 
tends to become comparatively shorter antero-posteriorly, and 
more obese in section. ‘Two individuals, each 32°5 and 33 
mm. in the above measurements, have respectively sectional 
diameters of 20 and 16 mm., demonstrating very great dif- 
ference in ventricosity. 
There is a marked tendency to rest-periods in its growth, 
producing, at intervals of about 5 millimetres, concentric steps 
from a half to one millimetre in depth. There are usually 
four of these in the adult; there may be six. Then they 
rapidly become closer and less valid, until the senile stage 
is reached, when the shell increases much in obesity and very 
little in altitude, and they are reduced to close-set concen- 
tric strie. 
The species is appropriately designated ‘‘sordidus,” for 
most shells show scarcely any colour markings on their dirty- 
white surface. But some are irregularly sparsely dotted with 
reddish-brown, in somewhat zigzag concentric lines, and are 
ornamented with four broad, curved, dark purple-brown 
flames, crossing the anterior and posterior marginal areas of 
the shell. - 
EX//7/ OThracia myodoroides, E. A. Smith. -— S30 
Thracia myodoroides, EB. A. Smith, Chall. Zool., 1885, vol. 
xiil., P 70, pl. vi., f. 6-6b. Type locality, off Hast Monceur Is- 
land, Bass Strait, in 88 to 40 fathoms: Pritchard & Gatliff, Proc. 
Roy. Soc. Vict., 1903, vol. xvi (n.s.), part i., p. 104. 
This shell was recorded for South Australia by Professor 
Tate under the name of Thracia modesta, Angas, from Tap- 
ley Shoal, in Trans. Roy. Soc. S. Austr., 1888, vol. xii., p. 67. 
It has been dredged alive at all depths between 8 and 
22 fathoms; most abundant at 20 to 22 fathoms. Valves 
are found at all depths up to 60 fathoms; most numerous be- 
tween 15 and 22 fathoms. It is fairly abundant, and is dis- 
tributed from Beachport westward through Spencer and St. 
Vincent Gulfs. 
As the shell grows larger, it changes in shape, becoming 
proportionally longer antero-posteriorly ; thus the type is 13. 
mm. long by 9°5 mm. high. Other individuals are 16 by 
10 and 18 by 11, whereas they should be 11:6 and 13:1 in 
height respectively. 

