Asking for a friend. These would probably fit better on archeology exchange, but as far as I know that kind of site does not exist yet.

First specimen, friend suspects it's some kind of Proetus. trilobite one

Second specimen, friend suspects the genus is Asaphus. trilobite two

Any help in narrowing the species identification down would be appreciated.


1 Answer 1


The first specimen seems more like Elrathia sp. Features noted that were similar are small eyes, small projecting genal spine (extreme left and right at the posterior margin of the cephalon), and strong anterior taper of the glabella (crown, or dome, between the eyes, tapers toward the nose). The pleural lobe (tail segment) is ovate along a lateral left-right axis and has few furrows. The specimen shows typical flattening (crushing) caused by the weight of the overburden during burial and lithification.

Although Proetus sp. shows features like Elrathia, the genal spines do not project as those in Elrathia. The glabella in Proetus is not strongly tapered, and the plural lobe, which has many furrows, is more elongated along the length of the shell rather than left to right.

The second specimen is harder to identify, but is similar in several aspects to Phacops sp, having pronounced eye-buds, and textured glabella. The specimen obviously appears small, perhaps a juvenile. An adult would be about 8.5 cm in length. This specimen is uncrushed.

Trilobites are called that because they have three lobes, namely, cephalon (head), thorax (central body), and pygidium (truncated posterior lobe). The animals molted regularly, so a single animal could produce a considerable number of shells over its lifetime. The fossilized remnants of the living animal, at death, are rarely if ever found. Trilobites had two shells, a dorsal shell, which is usually found, and a much softer ventral shell. This ventral shell, and the soft tissues of the trilobite animal, usually deteriorated after death so little is known about what trilobites looked like in life.

The following reference was consulted -

Easton, W. H., 1960, Invertebrate Paleontology, Harper and Row, New York.


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