The concept of many fossil taxa has been tightened over time, including Phacops.
As a result, Boeckops, Chotecops, Paciphacops, Prokops and Viaphacops have been erected as subgenera of Phacops, and are now widely regarded as genera in their own right.
Most recent, it was considered that some North-American and North-African species on the one hand and European species on the other hand differ sufficiently from each other to be assigned to separate genera.
As the type species is the European P. latifrons, the North-American species are now called Eldredgeops.
However, the previous assigned species, like Phacops rana, are still widely used among fossil collectors.
Eldredgeops has a raised ridge along the ventral margin of the cephalon, the glabella is more inflated, the lateral parts of the preoccipital ring are not round but rectangular, the palpebral area and palpebral lobe are larger than in P. latifrons, and there is no fold right behind the posterior vertical row of lenses, nor an isolated raised area just below the lenses.
Not all of these characters may differentiate between Eldredgeops and other Phacops species however.

During the Eifelian in the present-day Belgian Ardennes, several Phacops species developed from each other, the oldest being P. imitator, followed by P. fragosus, then P. latifrons and finally P. sartenaeri.
These species show a decrease in the number of lenses, which is a more widespread and recurring trend in many Phacopinae.

Fossils of Phacops salteri have been found in the trilobite-rich Late Emsian to Early Givetian Floresta Formation of the Altiplano Cundiboyacense, Colombia.
The concept of many fossil taxa has been tightened over time, including Phacops. As a result, Boeckops, Chotecops, Paciphacops, Prokops and Viaphacops have been erected as subgenera of Phacops, and are now widely regarded as genera in their own right. Most recent, it was considered that some North-American and North-African species on the one hand and European species on the other hand differ sufficiently from each other to be assigned to separate genera. As the type species is the European P. latifrons, the North-American species are now called Eldredgeops. However, the previous assigned species, like Phacops rana, are still widely used among fossil collectors. Eldredgeops has a raised ridge along the ventral margin of the cephalon, the glabella is more inflated, the lateral parts of the preoccipital ring are not round but rectangular, the palpebral area and palpebral lobe are larger than in P. latifrons, and there is no fold right behind the posterior vertical row of lenses, nor an isolated raised area just below the lenses. Not all of these characters may differentiate between Eldredgeops and other Phacops species however.
During the Eifelian in the present-day Belgian Ardennes, several Phacops species developed from each other, the oldest being P. imitator, followed by P. fragosus, then P. latifrons and finally P. sartenaeri. These species show a decrease in the number of lenses, which is a more widespread and recurring trend in many Phacopinae.
Fossils of Phacops salteri have been found in the trilobite-rich Late Emsian to Early Givetian Floresta Formation of the Altiplano Cundiboyacense, Colombia.
Phacops