106 
M. T. WARNE 
As in the Bairdiidae (Warne 1988), grada¬ 
tional and mosaic relationships abound within 
the Bythocyprididae. In this paper I attempt to 
refine the definitions of many bythocypridid 
genera. This is possible because members of the 
Bythocyprididae display a slightly greater degree 
of non-gradational species-group clustering than 
do the Bairdiidae. These bythocypridid species 
groups also have a more uniform environmental 
distribution than do presently recognised bair- 
diid genera. 
The Bairdiidae and the Bythocyprididae are 
not distinguished by consistent or simple mor¬ 
phological differences. A number ot forms, in 
particular those belonging to Bythopussella gen. 
nov., have carapace and soft part characters that 
are either intermediate in structure between the 
two families, or are unusually combined in the 
one form. For example, species such as Bytho¬ 
pussella aculeata (Muller, 1908), B. aff. aculeata 
ofMaddocks(1969)and B. sp. A(Cronin, 1983) 
have muscle scar patterns and compressed cara¬ 
paces typical of adult bythocypridids, but have 
lateral carapace outlines and anatomical fea¬ 
tures akin to juvenile bairdiids (Maddocks 1969, 
197 6 ). 
The late Tertiary bythocypridids of the Port 
Phillip and Western Port Basins have undivided 
or only weakly divided primary adductor muscle 
scars. This feature distinguishes these forms 
from the reniform bairdiids belonging to Papil- 
latabairdia, adults of which possess eight pri¬ 
mary adductor muscle scars (Bentley 1981, 
Warne, 1986, 1989). Orlovibairdia mooraboo- 
lensis sp. nov. is the only species described here 
that possesses both rimmed and unrimmed open 
normal pore canals. The other species have only 
unrimmed open normal pore canals. 
Subfamily Bythocypridinae Maddocks, 
1969 
Genus Bythocypris Brady, 1880 
Subgenus Bythocypris (Bythocypris) Brady, 
1880 
Type species. Bythocypris reniformis Brady, 1880. 
Remarks. The four species here assigned to 
Bythocypris (Bythocypris) have smooth, reni¬ 
form to subreniform or subrectangular cara¬ 
paces of varying thickness, inner lamellae of 
moderate size, adductor muscle scars that are 
usually undivided, and no marginal denticula- 
tion. Their carapaces are narrow in dorsal view 
but, unlike species ofAnchistrocheless.s., are not 
strongly differentially compressed or flattened 
along a narrow zone adjacent to the anteroven- 
tral and posteroventral margins. The reniform 
carapace of the type species, B. (B.) reniformis,is 
intermediate in shape between the subrectangu¬ 
lar carapace of B . (B.) subrectangulata sp.nov. 
and the subtriangular carapace of B. (Bytho- 
triangularia) subgen. nov. Thus, B. (B.) renifor¬ 
mis is not indicative of the maximum diver¬ 
gence in lateral outline between B. (Bythocypris) 
and B. (Bythotriangularia) but is closer to the 
subrectangular forms than to the subtriangular 
forms. Based on MaddocksXl969, 1973) draw¬ 
ings of B. (Bythotriangularia) species, forms 
assigned to this new subgenus may also have a 
greater propensity for secondary adductor 
muscle scar division than species of Bythocypris 
s.s. 
Species such as Anchistrocheles (intermedia 
Maddocks, 1969, A. barnharti Maddocks, 1976. 
A. bradyi Scott, 1905,/!. hartmanni Maddocks. 
1976, A. mcquadei Maddocks, 1916, Anchistro¬ 
cheles sp. Whatley & Downing, 1983 and 
Cythere acerosa Brady, 1868 more closely 
resemble Bythocypris s.s. than Anchisirochdcs 
s.s. in lateral outline. For example, A. bradyi is 
closer in overall carapace morphology to 
Bythocypris (Bythocypris) subrectangulata sp. 
nov. than it is to any species of Anchistrochdes. 
as the latter is here defined. Consequently, the 
seven species listed above are tentatively trans¬ 
ferred to Bythocypris (Bythocypris), even though 
they may ultimately warrant new generic or sub¬ 
generic status. These species possess slightly 
more compressed carapaces than many Bytho¬ 
cypris (Bythocypris) species. Unlike Anchistro¬ 
cheles, however, this compression is not re¬ 
stricted to a narrow zone adjacent to the ante- 
roventral and posteroventral margins but 
extends over a broader area of the carapace, 
frequently giving the entire anterior region a 
flattened, slightly extended appearance. It is not 
known whether this difference in the type of sur¬ 
face compression corresponds to any consistent 
differences in soft part anatomy. 
Forms such as Bythocypris IBythocypris1} 
bradyi appear to be transitional in carapace mor¬ 
phology towards deeper water species belonging 
to Zabythocypris , which have very compressed 
carapaces in dorsal view. This inferred relation¬ 
ship is supported by the tendency of some ante¬ 
riorly flattened Bythocypris (Bythocypris. 1 ! 
species to develop increased dorsal overlap. In 
Zabythocypris, greatly increased dorsal overlap 
