A survey for Geyer's Whorl Snail Vertigo geyeri on Cors Erddreiniog Site of Special Scientific Interest (SSSI)/ National Nature Reserve (NNR) and Cors Geirch SSSI/NNR in October 2016 failed to locate the snail. Survey locations were based upon previous records dating from 1985 to 2007 on Cors Erddreiniog and 1996 and 2008 on Cors Geirch. Losses from some former strongholds on Cors Erddreiniog are probably due to a lack of grazing, leading to the development of blanketing tussocks of Black Bog-rush Schoenus nigricans and Blunt-flowered Rush Juncus subnodulosus which have shaded out the open 'Carex-lawn' habitat required by the snail. This is most pronounced on Nant Isaf spring field (Compartment 13c) which has not been grazed for over 20 months. In other compartments, snail loss may be a consequence of over-grazing, or periods of under-grazing followed by cattle poaching of the remaining open areas. Similarly, Vertigo geyeri losses from known locations on Cors Geirch appear to be due to the development of a rank 'tussocky' sward that has reduced or eliminated the lightly-grazed 'Carex-lawn' habitat as a result of under-grazing. Voucher specimens from 2005 have been confirmed by the author of this report but no vouchers of the four specimens recorded in 2008 have been seen. As small populations of Vertigo geyeri can be easily overlooked, it is premature to declare the snail as extinct on Cors Erddreiniog and Cors Geirch. Additionally, areas which previously supported very small numbers of snails and not sampled in 2016 need to be surveyed soon. More regular surveys are required in order to advise on appropriate grazing regimes if Vertigo geyeri is found to be 'hanging on' on either site. If this is the case, then the development of simplified and affordable surveillance routines is suggested. Even in the apparent absence of Vertigo geyeri, it is vital that areas which previously supported the snail are managed appropriately. Grazing should be re-instated on Nant Isaf spring field as a matter of great urgency, and the current over-grazing of Compartment 9 on Cors Erddreiniog should be relaxed. On Cors Geirch, the area where Vertigo geyeri was first found in 1996 and again in 1998 and 2005 is too rank and grazing levels need to be increased to open up the seepages and the general sward.