Bolbolenellus
Bolbolenellus is an extinct genus of trilobites, fossil marine arthropods, with five species attributed to it currently. It can be easily distinguished from all other trilobites by the combination of the absence of dorsal sutures in the head shield like all Olenellina, and a distinctly bulbous frontal lobe of the raised axial area in the head called glabella. The species lived at the end of the Lower Cambrian.
Etymology
Bolbolenellus is the combination of Greek βολβός, and Olenellus, the rather distantly related genus to which all of the species were previously assigned. This refers to the bulb-like swelling of the frontal lobe of the glabella. The names of the species have the following derivations. B. altifrons from the Latin altus and from Latin frons, to express the species has a bulbous frontal glabellar lobe. B. brevispinus from brevis the Latin word for "short" and spinus the Latin word for "spine".B. groenlandicus is named for Greenland, where the species occurs. B. sphaerulosus from the Latin sphaerula.
Description
As with most early trilobites, Bolbolenellus has an only thinly calcified exoskeleton. Although most of the body is rather flat, the frontal lobe of the central area of the cephalon is prominent, bulbous, and may overlap the border at the front in dorsal view. It also shares crescent-shaped eye ridges, but these rise above the exoskeleton. As part of the Olenellina suborder, Bolbolenellus lacks dorsal sutures. Like all other members of the Olenelloidea superfamily, the eye-ridges spring from the back of the frontal lobe of the glabella. The posterior margin of cephalon is nearly straight or angles to the front on the outside of the intergenal spine or intergenal angle. The short genal spine protrudes opposite or posterior to the most backward side lobe of the glabella. There may be an intergenal spine. The frontal lobe of the glabella touches the border of the cephalon. The most backward tips of eye ridges segment has strongly enlarged side lobes, the spine on their end is not much enlarged compared to the spines of neighboring segments. The 14th segment carries a backward pointing axial spine that is approximately as long as the thorax axis. There seems to be no opistothorax.
Most other Biceratopsinae, i.e. Biceratops nevadensis, Emigrantia and Peachella and to a lesser extend Eopeachella have effaced cephalic features. Biceratops lacks genal spines. In Emigrantia the genal spines are longer than the cephalon and attach halfway down its side. Peachella has club-like genal spines. In Nephrolenellus the eye ridges extend outwards, the second pair of side lobes of the glabella are very narrow, the genal spines attach further to the front of the cephalon, T3 carries massive pleural spines, the axial spine on T14 is absent, and there is a prominent opistothorax.
Relations with other Biceratopsinae
The closest relative of the six species of Bolbolenellus is the genus Nephrolenellus. The other genera of the Biceratopsinae constitute the sister group.
Distribution
B. euryparia is present in the Upper Olenellus-zone of California.B. altifrons occurs in the Middle Olenellus-zone of the Northwest Territories.B. brevispinus has been collected in the Upper Olenellus-zone of Nevada.B. groenlandicus is found in Northwestern Greenland, questionably from the Upper Olenellus-zone.B. hermani occurs in the Upper Olenellus-zone of Vermont, of California B. sphaerulosus has been collected in the Olenellus-zone of the Yukon Territory, Canada.
Habitat
Bolbolenellus was probably a marine bottom dweller, like all Olenellina.