Undescribed Protolenines: Protolenus sp.

This is a new type of trilobite in the sub-family Protoleninae from Jorf Dahl (which includes the genus Protolenus and Hamatolenus).  I placed another specimen of the same trilobite in the genus Protolenus (Hupeolenus); however, this trilobite was initially placed in the genus Hamatolenus (Myopsolenus).  It has been placed back into the Protolenus genus, though not as a Hupeolenus.  I have done this as a result of learning more about the Hamatolenus and Myopsolenus: that this new type does not fit properly into the genus. 

The glabella is somewhat tapered in the front and has three distinct furrows directed back, and has parallel sides posteriorly.  This is similar to a sub-genus of Myopsolenus, however, other characteristics such as the genal spines have been decisive in taking this out of the Hamatolenus-Myopsolenus genus.  Though visible, the eye lobes and palpebral lobes are not well preserved.  Also, some of the pleurae seem fused together on the right side especially (see fourth photo).  The clear coat makes the usual orange limonite preservation of Cambrian trilobites from this area look brown.  It is a very large trilobite being six inches long, making it the largest of the Protolenines from Morocco known so far.  As a more well-preserved specimen became available for study the characteristics seemed at first to match with a Protolenus (Hupeolenus) more closely until a smaller trilobite with the same or very similar features was studied from my unidentified trilobite collection. 

The bottom three photos show this smaller trilobite that has characteristics that match this genus, and looks like a smaller version (juvenile) of the larger trilobite. The smaller trilobite shows sharper preservation of the cephalon, a close-up of which clearly shows marked glabellar furrows, palpebral lobes and the anterior border.

This new type can no longer be an H.Myopsolenus sp. (unknown species of this genus) because of the genal spines.  The glabella is similar to some trilobites in the H. Myopsolenus genus and the anterior border is also similar.  However, the genal spines are not similar not just because of the larger size, but also the base of the spine, the free cheek, is very different.  The spine base is larger and distally placed away from the cranidium so it is not like the Hamatolenus-Myopsolenus.  This gives the genal spines a wider arc and so are larger, longer and more robust than in H.Myopsolenus.

The overall preservation of this trilobite despite its size is not very good.  It looks to have suffered from decomposition before being fossilized so the details are hard to diagnose.

The cephalic border (above two photos) is unusually broad and prominent which is a salient characteristic of the genus Hupeolenus.  But it also has characteristics that are Myopsolenus-like such as the palpebral lobe position on the right, however, the left lobe is hard to discern.  It has three backwardly directed furrows on the glabella and a distinct posterior border furrow that forms an axial ring.

The pleural spines above are fused together because of poor preservation.  After examining this trilobite's thorax, the right and left sides do not match making it impossible to determine the number of thoracic rings it possesses.  This demonstrates that the preparation of the trilobite involved carving of the pleural spines.  Not all the pleurae are treated this way, but a few of the pleurae are useless for diagnosis due to separating the natural pleural furrows into separate pleurae. This is an important detail in regards to comparing with the smaller trilobite below. 

The smaller trilobite has a few classic Protolenus features shared by H.Myopsolenus such as the parafrontal band in front of the glabella that is unusually well preserved and a shorter (than Hamatolenus) palpebral lobe that does not reach the posterior furrow of the cranidium.  Unlike a typical described Myopsolenus it has long genal spines that are as long as the trilobite's thorax.  This maybe a juvenile of the same species as the larger trilobite.

This smaller trilobite has key characteristics that seem to make the case for being a juvenile of the larger trilobite, and that is why I conclude that instead of Hupeolenus this larger trilobite must be a new Protolenus genus related to this smaller specimen.  This smaller trilobite has a distinct anterior cepahalic border that is flattened in appearance just like the larger specimen.  It has a distinct posterior cranidial border furrow that includes a distinct furrow on the posterior part of the glabella that crosses the width of the glabella.  This characteristic is also found on the larger trilobite.  The glabellar furrows are backwardly directed and mirror the larger specimen.  The smaller trilobite (below) has what looks like fourteen thoracic segments. The fourteenth looks like it is partially tucked underneath.  The larger trilobite looks like it has fifteen thoracic segments, but this is not verifiable since there is questionable restoration of the thorax.  I conclude that this smaller trilobite is a juvenile of the larger trilobite, and because the smaller trilobite has distinct characteristics that are similar to the larger trilobite it must also be of the same genus and possibly of the same species. 

Kenjiro Hakomori 2014.11.11 (2020.5.22.)