66 WF. Ponder, D.J. Colgan, Т. Terzis, S.A. Clark, A.C. Miller 
D. harrisi is generally rather uniform in size in the northern spring groups (A and B) (Figs 16B, 
16D), but varies considerably in the other spring groups (С-Н) (Fig. 17). However, generally there is 
a considerable amount of variation in shell size and shape within this species (Appendix 2, Table 2; 
Figs 4, 5, 17; Ponder, 1989, figs 11.1A—E,G, 11.2A,D,E). The type population (Fig. 2A,B) is more 
similar to D. globosa in shell shape than most others (compare Figs 2A,B with 2H), although rather 
globose specimens are encountered in other populations (e.g. Fig. 4A,B,D). Mean shell size, in the 
36 measured populations, ranges from 1.5 to 4.1 mm (Appendix 2, Table 2) with considerable 
variance in some populations (Table 2, Fig. 17, and compare Figs 4A,B, D; 4C,E; 4F,G; 4H,I; 5А,В; 
5Е,С,Н), and many populations differ significantly (P«0.001) from conspecific populations in length 
and other dimensions and ratios. Overall there is a significant (P«0.001) difference in most shell 
dimensions and ratios between sexes. Comparisons with D. globosa show a significant (P<0.001) 
difference in all measured shell dimensions and their ratios. 
Several populations of D. harrisi have a proportion of individuals infected with parasites. In some 
samples the infected individuals are significantly larger than other members of the population but in 
others this is not the case. Eliminating parasitized individuals does not markedly alter the patterns of 
variation in shell size. 
Genus Fluvidona Iredale, 1937 
Type species: Hydrobia petterdi Smith, 1882. 
Remarks. The anatomy of the Wilson's Promontory species of this genus is described in detail by 
Ponder ef al. (1994). The species described below is included in Fluvidona because its radular, 
anatomical, opercular and shell characters agree with members of that genus in most respects. There 
are only two significant anatomical differences between this taxon and other species of Fluvidona. 
One is the position of the bursal duct which is located at the ventral end of the anterior edge of the 
bursa copulatrix in most individuals, whereas it opens in the middle of the anterior edge in other 
species of Fluvidona. The second character is the long, tapering penis with a narrow (not wide) base 
which is not markedly set off from the distal part of the penis as in other members of the genus. 
The genus name Fluvidona is used.following Ponder et al. (1994) but electrophoretic studies by 
one of us (S.A.C., in prep.) indicate that typical Fluvidona from northern NSW is generically 
distinct from the southern species attributed to this genus. 
Fluvidona centralia n. sp. 
Figs 2D,E, 6C,D, 7F-H, 8D, 9E,F, 12D, 18-19-20-21, 25. 
Etymology. Centralia — refers to the centre of Australia. 
Type locality. Spring Cd11, Dalhousie Springs, South Australia. 
Collection details of type material. Stn. D70, Spring Cd11, 26°24'40"S 135°30'29"E, small seepage 
on large mound, temp. 24°C, 9/5/1990, Coll. DC SC. 
Holotype, SAM, 18941; paratypes, SAM, 18942; AMS, C.201748. 
Diagnosis. With small, conical shell, prominent opercular pegs, 4—5 pairs of basal cusps on central 
teeth of radula, a ventrally located bursal duct and a narrowly tapering penis with a long, narrow 
base. 
Description. Shell (Fig. 2D,E, 18). Shell opaque, small (1.4-2.2 mm, mean 1.8 mm), conical, SW/ 
SL 0.56-0.67 (mean 0.62), AL/SL 0.36-0.46 (mean 0.40). Protoconch (Fig. 6C,D) of about 1.25 
whorls, distinctly punctate. Teleoconch of 2.7-3.5 (mean 3.1) convex whorls, sutures moderately 
