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tral margin strongly arched, roundly curving to the anterior 
margin. 
Surface with close-set concentric striz in the umbonal region 
gradually becoming linear sulci with increasing growth ; towards 
the front margin the flat ridges do not exceed *5 mm. wide, but 
they are somewhat unequal in width. The anterior and posterior 
slopes are ornamented with narrow, slender, minutely crenulated, 
radial threads ; the medial area is, however, obscurely radiately- 
lined. The right valve has two cardinal teeth and a lateral on 
each side, the left valve has one cardinal tooth and two laterals 
on each side. 
Dimensions of a large example.—Antero-posterior diameter, 
28; umbo-ventral diameter, 23 ; sectional diameter, 15 mm. 
Habitat.—As a beach-specimens collected in South Yorke- 
Peninsula by Messrs. Matthews and McDougall. Numerous 
single valves dredged by Dr. Verco, from 15 and 22 fathoms in 
Investigator’s Straits; and from 30 fathoms off Corney Point, 
Spencer-Gulf. 
A ffinities—This species has been known to me for some years 
past, but as the condition of the specimens did not permit of 
detailed definition, it had been regarded tentatively as the senile 
stage of LZ. Tatei, Angas. Some of the specimens recently obtained 
by Dr. Verco permit a critical comparison to be made. In outline 
the new shell is more comparable with Z. obliqua, Reeve, but that 
shell is decussated throughout with radial and concentric strie. 
L. Tatei, which does not much exceed 8 mm. in the umbo-ventral 
diameter, is ornamented with linear raised concentric lines, with 
broad intervening furrows, tessellated by conspicuous radial 
ridges ; whilst the umbonal portion of “. perobliqua, correspond- 
ing in area with a large valve of ZL. Yatei, is marked with close- 
set concentric strie, and the lateral borders only with radial 
threads. As yet no examples of Z. perobliqua have been obtained 
so small as the largest Z. Tatei, but the smallest of them show an 
obliquity which is not presented by the latter. 
Lueina paupera, spec. nov. Pl. i., fig. 6. 
Shell quadrately- and somewhat obliquely- oval, equivalve, very 
inequilateral, solid, dirty-white, very finely ridged concentrically ; 
the concentric ridges very thin, inconspicuously elevated and 
distant, the interstices smooth; at about three-fourths to the front 
they become closer together and thicker ; there is no trace of 
radial ornamentation. 
The antero-dorsal margin is nearly straight, and rapidly 
descending; the post-dorsal margin is arched, and abruptly joins 
the much-rounded posterior margin ; ventral margin considerably 
arched. 
