
656 RECORDS OF THE S,A, MUSEUM 
Remarks: The Recent European genotype of Nucula, N. nucleus Linne, 
differs from recent and fossil Australian Eunucula whieh the author of the genus 
poiited out has a ‘notably oblique chondrophore; above which the teeth become 
much smaller and the angle of opposition of the two rows of teeth is searcely 
marked ; further, the edge of the European shell is strongly denticulate, whereas 
ours is smooth.’’ A complex group of Recent, shallow and deep water species 
belonging to this genus have been described, the localities ranging from New 
Guinea to Queensland, Victoria, South Australia and Tasmania, Many have 
heen lumped under the familiar name N. obliqua Lamarck, a Southern Tasmanian 
living species. 
ARCA NEGATA sp. Noy, 
Plate xx, fies. 11, 12. 
Shell trapeziform, rounded in front, obliquely truncated posteriorly ; hinge 
lines straight; umbones anterior, distant, acute; ventral margin with an almost 
median byssal gape; a sharp ridge runs from the umbo to the posterior ventral 
angle; anterior to the angle the sculpture consists of close fine radial ribs abruptly 
changing to less numerous wider radial ribs on the larger anterior portion. 
Height 11 mm., length 24 mm, (holotype). 
Loc.: Bore 64, 385-395 feet, holotype, Adelaidean. 
Remarks: This species, which may grow to twice the size of the holotype, 
somewhat resembiles the Recent Arca navicularis Bruguiere 1792 from Amboina, 
related to Arca subnavicularis Iredale 1939 from North Australia. The Pliocene 
fossil here deseribed as A. negata is nearest to A. pseudonavicularis Tate 1886 
from the Adelaide Bore, Janjukian, but is differently sculptured. The new species 
is a true Arca aceording to Opinion 189 of the International Commission on Zoo- 
logical Nomenclature which decided, ‘‘ Under suspension of the rules: 
(1) To set aside all type designations of Arca Linnaeus 1758, Syst. Nat, 
(Ed. 10) 1, 698 (Class Peleeypoda, Order Filibranehia), made prior to 
the date of this opimion ; 
and (ii) To designate Area noae Linnaeus 1758, Syst. Nat. (Ed. 10) 1, 693, as 
the type of Arca Linnaeus 1758.”? 
The genus Nawicula Blainville 1825, introduced for the same genotype, has 
thus become a direct synonym, as does Byssvarca Swainson 1833, Arca Gray 1847, 
Cibola Moerch 1853, Daphne Poli 1791 (not Mueller 1776) and Daphnoderma 
Poli 1795. 
Six Recent Australian species are deseribed from Northern Australia. 
