but almost parallel to the midline. The back of the eye-ridges is opposite the most backward ring of the glabella (L0 or occipital ring). Genal spines are 6-8 times as long as L0. The outer furrows of the glabella are parallel to the midline between the back of the cephalon and the furrow between side lobes L2 and L3. The thorax is 3 times as wide as the axis at the 3rd segment. Mesolenellus can be distinguished from the sister-genus Mesonacis, where the back of the eye-ridge extends only to the most backward side lobes (L1), genal spines are only 1-5 times as long as L0, and the glabella widens forwards along L1 and L2. Except for in Mesonacis fremonti the curved eye-ridges are at an angle of 15°-20° with the midline. A third genus Olenellus, that constitutes the second subfamily of the family Olenellidae differs from Mesolenellus in having genal spines 4-5 times as long as L0, the glabella widens forwards along L1 and L2, and the thorax 4-4½ times wider that the axis at the 3rd segment. Key to the species References External links Trilobite info Olenellidae Redlichiida genera Cambrian trilobites Cambrian trilobites of Europe Cambrian genus extinctions