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Records of the Australian Museum (2009) Vol. 61 
Fig. 5.A-F, Drepanodus arcuatus Pander, 1856. All from sample WCB705/133. A,B, Sa element; (A), CPC39811, lateral view (IY126-002); 
(B), CPC39812, lateral view (IY126-003). C,D, Sd element; (Q, CPC39813, inner lateral view (IY127-028); (D), CPC39814, inner lateral 
view (IY127-022). (E), Pb element, CPC39815, inner lateral view (IY126-001). (F), Pa element, CPC39816, outer lateral view (IY126-005). 
G-P, Drepanoistodus sp. cf. D. nowlani Ji & Barnes, 1994. (G), M element, CPC39817, WCB705/243, anterior view (IY129-005). H,I, 
Sa element; (//), CPC39818, WCB705/133, lateral view (IY126-004); (I), CPC39819, WCB705/133, lateral view (IY127-016). (7), Sb 
element, CPC39820, WCB705/133, inner lateral view (IY127-029). K,L, Sc element; (K), CPC39821, WCB705/133, outer lateral view 
(IY 126-008); (L), CPC39822, WCB705/133, outer lateral view (IY129-027). (M), Sd element, CPC39823, WCB705/133, inner lateral 
view (IY 127-030). N,0, Pa element; (AO, CPC39824, WCB705/243, inner lateral view (IY129-025); (O), CPC39825, WCB705/243, outer 
lateral view (IY129-026). (P), Pb element, CPC39826, WCB705/243, outer lateral view (IY129-006). Scale bars 100 pm. 
van Wamel (1974), Lindstrom (in Ziegler, 1977), Stouge 
& Bagnoli (1999), Zhen et al. (2003), Nicoll & Ethington 
(2004) and Zhen et al. (2005). McTavish (1973) described 
A. deltatus and several other species of Acodus from the 
Emanuel Formation of the Canning Basin, and suggested a 
seximembrate apparatus for A. deltatus including prioniodi- 
form (= P of our interpretation), ramiform (trichonodelliform 
= Sa, gothodiform = Sb, cordylodiform = Sc, and tetraprio- 
niodiform = Sd of our interpretation), and oistodiform (= M 
of our interpretation) elements. Based on the stratigraphical 
distribution and morphological changes of various Acodus 
species recognized in the Emanuel Formation, McTavish 
(1973, fig. 7) indicated that both Prioniodus and Baltoniodus 
might have evolved from Acodus. Some authors went even 
further by attributing A. deltatus to either Prioniodus (van 
Wamel, 1974) or Baltoniodus (Bagnoli etal., 1988). In their 
revision of A. deltatus , Bagnoli etal. (1988) considered it to 
have a seximembrate apparatus without an Sa element, and 
included in this species some specimens from the Emanuel 
Formation illustrated by McTavish (1973). Subsequently 
Stouge & Bagnoli (1999) indicated that forms referred to A. 
deltatus by McTavish (1973), Ethington & Clark (1982) and 
