Peronopsis interstrictus (White, 1874)
Middle Cambrian (505 Million Years)
Bolaspidella-zone; Wheeler Shale Formation, Antelope Spring, House Range, Utah
These diminutive, and blind, Agnostid trilobites are some of the most bizarre looking in the trilobite record. Found commonly in what is known as the "Bolaspidella Zone", for the mass quantity of Bolaspidella specimens found amongst the Elrathia and other species known from the Cambrian fauna.
Traditionally, trilobites are subdivided into two major groups: the polymeroids and the agnostoids. Polymeroids are garden-variety trilobites. They have a multisegmented thorax; they usually possess eyes; and they can be macropygous, isopygous, or micropygous (the head is smaller than the tail, the head & tail are equal-sized, or the head is larger than the tail). Agnostoids have a two-segmented thorax only; they are all blind; and they are all isopygous (the heads & tails are equal-sized). Agnostoids are usually quite small.
Many modern arthropod phylogenetic studies suggest that agnostoids should be excluded from the trilobites.
Size : 1 x 0.5 cm
1 inch = 2.54 cm