Key To The Species
| 1 | The curved eye-ridges are at an angle of 15°-20° with the midline. Except for the third thorax segment, the spine on the side lobes (or pleural spine) is approximately a quarter of the length of the segment, halfway between the spine and the axis. → 2 |
|---|---|
| - | The curved eye-ridges are at an angle of 0°-5° with the midline. The pleural spines of T1-T2 and T4-T14 are at least half as long as the segment. → Mesonacis fremonti |
| 2 | The furrows between the lobes of the glabella are faintly incised. The frontal lobe of the glabella (L4) is connected with the border surrounding the cephalon with a short ridge on the midline (the so-called “plectrum”). → Mesonacis bonnensis |
| - | The furrows between the lobes of the glabella are prominently incised. A plectrum is absent or very faint. → 3 |
| 3 | The frontal lobe (L4) of the glabella intersects the anterior border furrow. The furrow between the second (L2) and third (L3) side lobes (S2) is transverse. The furrow between the occipetal ring (or posterior lobe, L0) and the first pair of side lobes (L1), indicated as S0, is joint at midline. → 4 |
| - | L4 does not intersect the anterior border furrow. S2 curves, so that it is further to the back at midline. S0 consist of two furrows that do not joint at midline. → 5 |
| 4 | S2 contacts the furrow that defines the glabella (or axial furrow). The posterior rim of the cephalon (or intergenal angle) curves forwards midway between the posterior tip of the eye ridge and the genal angle. Frontal glabellar lobe (L4) as wide as the occipetal ring (L0). → Mesonacis hamoculus |
| - | S2 does not contact the axial furrow. The intergenal angle is located at three quarters the tip of the eye lobe and the genal angle. L4 wider than L0. → Mesonacis cylindricus |
| 5 | The frontal margin of the macropleural segment (T3) flexes forwards at at least 110° with the midline. The second (L2) and third (L3) pair of glabellar side lobes are not divided by a furrow at midline (or S2 does not join at midline). → Mesonacis vermontanus |
| - | The frontal margin of T3 flexes forwards no more than 95°. S2 is joined at midline. → Mesonacis eagerensis |
Read more about this topic: Angustolenellus
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