The presence of the genus Eusarcus in the Frankfort fauna is demonstrated by various characteristic parts of the integument, viz, two forms of carapaces, cordiform metastomas so typical of Eusarcus, extremely broad and short tergites, the long conical postabdominal segments, a telson, and fragments with the characteristic ornamentation. The metastomas are probably the most conclusive of these, no other genus having furnished singularly broad and short subtriangular plates.
The two species here described are for the present entirely based on the carapaces and the other parts of the integument are noted below.[1]
The genus hence comprises the following species:
| Eusarcus scorpionis Grote & Pitt | E. raniceps (H. Woodward) | |
| [incl. E. giganteus Grote & Pitt] | E. scoticus (Laurie) | |
| E. newlini (Claypole) | E. acrocephalus (Semper) | |
| [incl. E. ingens (Claypole)] | E. simonsoni (Schmidt) | |
| E. punctatus (Salter) | E. longiceps nov. | |
| E. scorpioides (H. Woodward) | E. triangulatus nov. | |
| ? | E. obesus (H. Woodward) |
- ↑ Other appendages referable to Eusarcus in the Frankfort shale. We reproduce three metastomas which, by their cordiform outline indicate that they probably belong to a type that is either identical or closely related with Eusarcus. The smallest of the three [pl. 84, fig. 10] is covered with flat, round tubercles that agree with those of the integument of E. scorpionis. Another possesses small, granular tubercles [pl. 84, fig. 11].
Our collection also contains the characteristic long conical tail segments and in one case a segment with attached curved telson spine; this and a few tergites suggest the preabdomen of a Eusarcus.
margins making horseshoe-shaped impressions, is characteristic of Eusarcus as fully stated in the generic description. The clear photographs of the type of the Russian species show that the general outline and the form of the attached last leg possess the characteristics of Eusarcus. The detached part is not a leg as surmised by Schmidt but the scorpioid slender postabdomen of Eusarcus, and furnishes another character typical of that genus. As to the "Dorsalfurchen" we have the impression that they are accidental. Less pronounced furrows have been noticed by us in various specimens of Eurypterus remipes and other species.
The abdomen appears relatively a little longer than in our species of Eusarcus, possibly through a pulling apart of the segments in anteroposterior direction.
