Key to the Azorean species of Trechus

1 Apical angle of elytra rounded.............. 2

– Apical angle of elytra pointed or sharp angled......... 6

2 Larger species, length w 3.5 mm; lateral margins of pronotum markedly sinuated before the basis, degree of pigmentation variable......... 3

– Length 3.0– 3.2 mm; lateral margins of pronotum hardly sinuated before basis; clearly dark pigmented species........... torretassoi Jeannel

3 Depigmented with a convex and ovalate facies; 3rd antennomere longer than 2nd...................... 4

– Body pigmentation variable with lighter parts; with a transverse and depressed body; 3rd antennomere subequal to 2nd............. 5

4 Aedeagus with apex of lamella slightly blunt; only in Pico.. picoensis Machado

– Aedeagus with apex of median lobe deeply curved upwards (figure 3a); only in Faial................ oromii new species

5 Pronotum cordiform and highly transverse (index W/L ~ 1.35), with lateral furrow very narrow............ terrabravensis new species

– Pronotum index W/L ~ 1.12; lateral furrow larger...................... montanheirorum Oromí and Borges

6 Apical angle of elytra sharp (sometimes notched), forming a small protruding point; total length 3.6–4.3 mm .......... terceiranus Machado

– Apical angle of elytra sharp (forming a right angle). Size v 3.5 mm .... 7

7 Slightly pigmented on elytra and pronotal disc; aedeagus in lateral view with apex of median lobe more or less straight and pointed (figure 2a); right paramere with four setae (figure 2b).............. pereirai new species

– Depigmented; aedeagus in lateral view with apex of the median lobe sharpened and slightly upward curved (figure 4a); right paramere with five setae (figure 4b)............ jorgensis Oromí and Borges