Christiansen & Bellinger (1998) suggested that all records of Sinella caeca from the UK probably refer to the closely-related species Sinella tenebricosa Folsom, 1902. The map shows the localities of all the Sinella 'caeca' which I have checked. The sites were 'London Zoo', 'Kew hothouse' and 'Wisley, water tank'. All specimens were definitely Sinella tenebricosa.
     Sinella tenebricosa has a pointed tenant seta on the outer distal tibiotarsus (Figs. 1 and 2) - this spine is distinctly expanded at the tip in Sinella caeca. In Sinella tenebricosa, the mucronal spine reaches to the tip of the mucro, and the non-crenulated region of the dorsal side of the distal part of the dens is only slightly longer than the mucro (Fig. 3). In Sinella caeca, the mucronal spine is much shorter and the non-crenulated region of the dens much longer than in Sinella tenebricosa. Thus Sinella caeca should probably be removed from the checklist.
     Sinella tenebricosa is a synanthropic species originally from the Orient which is likely to turn up in many more localities.

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Fig. 3 (above): Furca of Sinella tenebricosa collected from London Zoo in January 1956 by Peter Lawrence. The mucronal spine reaches the tip of the mucro. The non-crenulated region of the dens (*) is short (only about the same length as the mucro).

Fig. 1 (above left): Foot and tibiotarsus of the third leg of Sinella tenebricosa collected from a water tank at Wisley in July 1936 by W.M. Davies.
Fig. 2 (above right): The same specimen at a different level of focus showing the pointed tenant seta.