Zhen & Nicoll: Canning Basin Serratognathus bilobatus Fauna 
15 
Material. 457 specimens from three samples (Table 1). 
Remarks. The species as revised by Lofgren (1997) 
possesses a septimembrate apparatus (including makellate 
M and drepanodiform or paroistodiform S and P elements), 
which can be distinguished from the other species of 
Paroistodus by having prominent lateral costae on the sides 
of its constituent elements. Zhen et al. (in press b) preferred 
to describe the S and P elements as paroistodiform in the 
Paroistodus species which show a sharp anterior costa 
extending basally into the basal cavity and forming a ridge¬ 
like structure (Zhen et al., 2007b, p. 137) at the anterior 
end of the basal cavity. However this character is not shown 
in the material of the two Paroistodus species (similar to 
Paroistodus sp. recently documented from the Honghuayuan 
Formation in South China) reported herein from the Emanuel 
Formation, although the anterior part of base often exhibits a 
zone of recessive basal margin (Figs 7A-C, 8H). Paroistodus 
parallelus occurs abundantly in the Emanuel Formation, 
where it is found in association with P. proteus although the 
latter is rare (Table 1). 
Paroistodus proteus (Lindstrom, 1955) 
emend. Lofgren, 1997 
Fig. 8A-K 
Drepanodusproteus Lindstrom, 1955: 566, pi. 3, figs 18-21, 
text-fig. 2a-f, j. 
Paroistodus proteus (Lindstrom).—Lofgren, 1997: 922-923, 
text-figs 3H-N, 4L-AB {cum syn.)', Zhen et al., 2007b: 
136, 137, pi. 5, figs 1-11 ( cum syn.). 
Material. 30 specimens from three samples (Table 1). 
Remarks. Paroistodus parallelus is relatively rare in the 
Emanuel samples, and can be easily differentiated from as¬ 
sociated P. parallelus mainly by lacking a prominent costa 
on the lateral faces. Paroistodus proteus was revised by 
Lofgren (1997) as having a septimembrate apparatus. After 
a review of previously reported occurrences of this species in 
the Honghuayuan Formation and other coeval stratigraphic 
units in South China and comparison with Baltic material of 
P. proteus, Zhen et al. (2007b) concluded that Paroistodus 
is represented in the Honghuayuan Formation by a rare 
form that they identified as Paroistodus sp. It differs from 
P. proteus in having a smooth lateral face without a carina 
and having a more open basal cavity which lacks the distinc¬ 
tive so-called paroistodiform character. The material from 
the Emanuel Formation is transitional between typical P. 
proteus from the late Tremadocian to Floian of Balto-Scandia 
and Paroistodus sp. from the Honghuayuan Formation of 
South China. It is comparable with P proteus in having a 
prominent carina (Fig. 8A-E) or even a weak costa (Fig. 
8J) on the lateral faces, but similar to Paroistodus sp. from 
the Honghuayuan Formation in lack of the paroistodiform 
feature. As mentioned above, absence of the paroistodiform 
character in species of Paroistodus co-occurring in the 
Emanuel Formation may indicate that this feature is caused 
by ecological adaption rather than as a phylogenetically 
significant trait for Paroistodus. Interestingly, P. proteus 
from the Emanuel Formation of Western Australia and 
from the Latorp Limestone and Tpyen Shale of Sweden 
and Paroistodus sp. from the Honghuayuan Formation of 
South China come from three contrasting ecological/sedi- 
mentological settings; they may represent three populations 
or subspecies of P. proteus. The typical latest Tremadocian 
and early Floian P. proteus- bearing successions in Sweden 
(e.g., Diabasbrottet area) were deposited in the outer shelf 
settings of the Cold Domain (Bergstrom et al., 2004), and the 
mid-upper part of the Emanuel Formation might be largely 
deposited in deep subtidal settings, while the Honghuayuan 
Formation with Paroistodus sp. apparently represents typical 
shallow subtidal environments. Therefore, in consideration 
of the relationship between their morphological variation 
and their ecological/geographical distributions, the material 
from the Emanuel Formation is considered as conspecific 
with type material of P. proteus, and Paroistodus sp. from 
the Honghuayuan Formation (Zhen et al., 2007b) might be 
better treated as a separate subspecies of P. proteus. 
Prioniodus Pander, 1856 
Type species. Prioniodus elegans Pander, 1856. 
Prioniodus adami Stouge & Bagnoli, 1988 
Fig. 6G-L 
Prioniodus sp. nov. C McTavish, 1973: 47, pi. 3, figs 4-6, 
?11, 16, text-fig. 6f, g, i, ?j, k. 
Prioniodus adami Stouge & Bagnoli, 1988: 132, 133, pi. 
11, figs 5-13 {cum syn.); ?Albanesi et al., 1998: 155, pi. 
10, figs 1-3; Johnston & Barnes, 2000: 36, pi. 16, figs 
9, 10, 13-16, 19; Pyle & Barnes, 2002: 110, pi. 26, figs 
19-21. 
Material. Four specimens from two samples (Table 1). 
Remarks. Based on a large collection from Bed 9 of the 
Cow Head Group of western Newfoundland, Stouge & 
Bagnoli (1988) established P. adami as having a septi¬ 
membrate apparatus (pastinate Pa, and Pb, ramiform S 
and geniculate M elements), and also included in it the 
material from the Emanuel Formation that McTavish 
(1973), ascribed to Prioniodus sp. C except for the oisto- 
diform element (his pi. 3, fig. 11, text-fig. 6j) which bears a 
short, adenticulate inner lateral process. Prioniodus adami 
is characterized by bearing small, closely-spaced denticles 
on the long posterior process of the S and P elements, as 
well as on the anterior and outer lateral processes of the P 
elements and the inner lateral process of the M element. 
The Pa element (Fig. 6G, H) from the Emanuel Formation 
is identical with those illustrated by McTavish (1973, pi. 
3, figs 5, ?16), but exhibits less closely spaced denticles 
on the processes in comparison with the holotype (Stouge 
& Bagnoli, 1988, pi. 11, fig. 8). The M element from the 
Cow Head Group shows a long adenticulate outer lateral 
process and a long, denticulate inner lateral process with 
small, closely-spaced denticles, similar to those on the 
processes of the P and S elements, but no M element has 
been recovered from the samples of this study. 
