Dalhousie 5 prings hydrobiids S 
i |} б lii à TT SH e 
A 
A б YS < 
$ SN 
11 X e 
M X Ж 
| № 
e e 
S : e 
` av 
m Ih // 
tet SCH d 
së À 
: м, 
"m 
qu 
poet 
5. 
Figure 19. Radulae of Fluvidona centralia. AC. Spring El (station D62), С, detail of central teeth. B,D. Paratype, 
Spring Cd11 (station D70), D, detail of central teeth. Scales A,B – 0.02mm, C,D — 0.005mm. 
b having the bursal duct opening antero-ventrally to the bursa and in having a gradually tapering 
Penis with a narrow base. 
Allozyme electrophoresis. 
Gene frequency tables are given for the three taxa in Appendix 3. Our results confirm that the 
Snails are grouped into two lineages, Dalhousia and Fluvidona. Dalhousia is the dominant 
Component and is widespread throughout the Dalhousie Spring system. The second group was found 
In only seven localities, predominantly in the small seepages and in the lower, swampy outflow from 
à large spring (Е1). Allozyme mobilities and activities differ so much between these two groups that 
no evolutionary relation between them can be discerned. Consequently, the allozymes within each 
Stoup were named and analysed separately. 
alhousia can be sub-divided into at least two genetic species recognised on the basis of 
Characteristic suites of allozymes. D. globosa is characterised by very high frequencies of the Lap 2, 
8m-2 3, Sdh-] | and Sdh-2 2 alleles, and a high frequency of the брі 2 allele. These allozymes are 
Virtually absent or found in very low frequencies in D. harrisi which is characterised by high 
Iequencies of Lap 3 and Pgm-1 4, which are virtually absent іп D. globosa, Sdh-1 2 and Sdh-2 1. 
With the exception of samples from Са8 and С42 springs, where there appears to be a breakdown of 
'Solating mechanisms, there were very few heterozygotes at the Lap or Pgm loci which comprised a 
Characteristic allele from each of D. harrisi and D. globosa. Individual snails were scored and 
