Hamatolenus (Myopsolenus) magnus (2)  Hupe 1953

According to Geyer's 1990 revision (see index page for reference) Hamatolenus is characterized by palpebral lobes that are longer than that of Myopsolenus and reaches the posterior border of the cephalon, nearly opposite of Hupe's original 1953 diagnosis (Treatise, pg O211) where Hamatolenus is characterized by palpebral lobes that do not reach the posterior furrow of the cephalon.  Also, Geyer includes more description about the Myopsolenus, and what makes it different from the sub-genus Hamatolenus.  He includes many more photos of the sub-genus and its cephalon (head area) making other factors such as glabella size and the palbebral lobes and their disposition more clear.

So though I have stuck with Hupe's original diagnoses for both sub-genuses' Hamatolenus and Myopsolenus for the most part, other factors Hupe never mentioned do play a part in deciding which sub-genus to place these specimens in.  The glabella on this particular specimen is very large with no apparent pre-glabellar field which is not uncommon among the sub-genus Myopsolenus.  Very rarely, even in this instance, will there be a traceable para-frontal band as a result of the large glabella that often impinges on the anterior cephalic border. 


In the above photo the palpebral lobe does not reach the posterior furrow of the cephalon as in Hupe's description of Hamatolenus on one side. Interestingly, it appears that the palpebral lobe does not reach the posterior furrow of the cranidium on the left side but does so on the right side.  The palpebral lobes are parallel to the anterior edge of the cephalon as the close-up shows very well and also distally away from the glabella--and the lobes do not have the "s" shape of H. moroccanus.  Notice that the eye ridge is visible along with the palpebral lobe on this very well preserved specimen.  This specimen also has a large glabella that is wider than that of the typical H. Hamatolenus species.  The pygidium is somewhat crushed (below) and not well-preserved unlike the rest of the trilobite.  So in this case the preponderance of the characteristics shows that this is most likely a sub-genus Myopsolenus.

Kenjiro 2015.6.9. (revised 2020.5.20)