Nicholas Range, Tas, -41.5417 148.0786 ±25 m (GPS), 570 m a.s.l., 14 May 2012, W. Clarkson and L. Clarkson, QVM 23:53867 (ex QVM 23:52247).

3 males, details as for holotype, QVM 23:52247.

21 males and 4 females (see Suppl. material 1 for details).

Very similar to Tasmaniosoma decussatum, but without a setose sternal tab adjoining leg 7, with the anterolateral telopodite process prominently notched, with the solenomere tabs curving posteriorly and less deeply separated, and with the medial process tongue-like and curving posterobasally, rather than forming a rounded, mediolaterally flattened, tab-like solenomere extension as in Tasmaniosoma decussatum.

Male/female approximate measurements: length 12/11 mm, midbody paranota width 1.4/1.4 mm, maximum vertical diameter 1.1/1.1 mm. Live and freshly preserved adults with yellowish ground colour (Figs 1B, 1E), antennae and distal podomeres pale reddish brown, reddish brown transverse streaks or cellular margins anterior to transverse furrow and near posterior margin of metatergite, and laterally on prozonites and below paranota. Colouring fades in alcohol; long-preserved animals entirely decoloured or more or less uniformly pale yellowish white.

Non-gonopodal features in males mostly as for Tasmaniosoma anubis sp. n., but head moderately setose; antennal sockets separated by ca 1.5× socket diameter; overall ring widths 6>5>(4,head)>2>3>collum; rings 8-16 distinctly elongated; ring 2 ventrally on either side with wide, shallow pit, the anterolateral margin well-defined; metatergites with indistinct low tubercles medially; midbody legs with tarsus ca 1.8× as long as femur; brush setae on coxa/trochanter, prefemur and femur of anterior legs; legs 6 and 7 bases (Fig. 2B) well- and equally separated; no setose sternal tab by leg 6 or leg 7, but sternite by leg 7 base slightly produced as rounded bumps.

Gonopod aperture ovoid, ca 1/2 as wide as ring 7 prozonite, posterolateral margin raised. Telopodites (Figs 5C, 6) almost straight, parallel; extending to leg 6 bases when retracted. Telopodite with shallow concavity over most of posterior surface, the margin continuing as posterior margin of posterobasal shelf; anterior surface strongly and broadly ridged. Telopodite divided at ca 2/3-3/4 height into four processes: (a) long, rod-like, tapering, apically rounded lateral process directed distally and slightly posteriorly; (b) large anterolateral process curving posteriorly with distinctive, V-shaped notch on anterior edge, S-shaped distal to notch with acuminate apex directed distally and slightly laterally; (c) posteromedial solenomere developed as parallel, subquadrangular, transverse tabs separated by narrow slit, curving posteriorly; (d) tongue-like medial process curving basally and directed slightly medially. Sparse setae posterolaterally to ca 1/2 telopodite height, with small, separate patch of fine, short setae on posterior surface ca 1/3–1/2 telopodite height. Prostatic groove running up medial surface of telopodite, curving laterally across posterior surface in slit between solenomere tabs, then running along lateral margin of more basal tab to open near medial corner of tab (Figs 5C, 6).

Female about as robust as male but shorter, with posterior rings not elongated; legs more slender and prefemora and femora not swollen. Epigynum ca 1/3 width of ring 2, posterior margin produced medially as low trapezoid with irregular margin. Cyphopods not examined.

Eucalypt forest over ca 100 km² north and east of Fingal, Tasmania, with an outlying record near the town of Scamander on the east coast (Figs 5A, 7A). Co-occurs with Tasmaniosoma barbatulum, Tasmaniosoma nicolaus sp. n. and Tasmaniosoma orientale in bark and leaf litter in the Nicholas Range.

Latin inter (between) + fluminum (genitive plural of flumen = river); adjective. The largest populations of this species are found between the upper South Esk and Break O’Day Rivers.

The gonopod telopodite structure of Tasmaniosoma interfluminum sp. n. is remarkably similar to that of Tasmaniosoma decussatum, the two differing only in the details noted above in Diagnosis. Another difference is a setose sternal tab adjoining the base of leg 7: present in Tasmaniosoma decussatum, absent in Tasmaniosoma interfluminum sp. n. I am unable to distinguish the two species in the field.