On pg. 178 in discussing the development of *-Vtsm- I give *retsmos as the pre-form for rēmus 'oar' and cite the inscriptional form TRIRESMOS (ILLRP 319) in support of this. But both the reconstruction and the evidential value of the form TRIRESMOS are highly dubious.
First, TRIRESMOS comes from the notorious Columna Rostrata inscription of Duilius. This inscription was ostensibly composed by Gaius Duilius the consul of 260, but the actual physical monument certainly does not date to the 3rd century BCE, but from some centuries later. The crucial question, however, is whether the text as we have it is (1) a faithful copy of the original, (2) a flawed but honest attempted a reproducing the original, or (3) an ancient falsification made up on the basis of what a scholarly Roman of some centuries later would have thought Duilius should have written. If anything like the third hypothesis is correct, then the S of TRIRESMOS is worthless since it could have been inserted on the model of CL dūmus 'thorn bush' : VOL dusmos (preserved in Livius Andronicus' 31.35 dusmo in loco 'in a thorny place') rēmus : X, X = resmos. The Columna Rostrata does have the form PRIMOS from < *prīsmos, but that in itself does not prove that TRIRESMOS is a false archaism since one need only assume that the modernization was carried through inconsistently or maybe even that *-Vsm- lost its s before *-VCsm-. Nevertheless, this form in this inscription is a very thin reed to support any etymological hypothesis about rēmus.
Second, the root in question is *h1erh1- 'row' (Ved. aritá: 'rower', Grk. ἐρέττω 'I row', < *h1erh1-t-jo:, etc.) and nowhere but in Greek is there any evidence for a t-extension of the root—and the unextended from of the root is still attested in Myc. e-re- /erehen/ 'to row'. The Latin form points to a schwebeablauting e-grade pre-from *h1reh1-mos. A pre-from *h1reh1-smos would also be possible, as I mention in n. 20, but given the dubious nature of TRIRESMOS there is no strong reason to favor it. See Vine 1993:126.
So are there any good cases of *-Vtsm-? There don't seem to be any quoted by the usual suspects (Meiser, Sihler, Leumann, Sommer, Meillet and Vendryes), but I'd be highly surprised if the outcome was anything other than -V:m-. Could pōmum 'tree-fruit' be from *potsmo- 'what falls' or 'what one seeks'? I have selfish reasons for preferring this to the standard *po-emo- 'what is taken away'. See Weiss 2010:229. But I wouldn't insist on it.