The type of the original description [pl. 36, fig. 4] is a small broadly triangular carapace so unusually broad that its length to width is as 2 : 3. The lateral margins in their general direction converge to the protruding front of the carapace and possess a gently sigmoidal curvature, the posterior two thirds resembling projecting cheeks while the anterior third is concave. The postlateral angles are acute. The carapace is highest between the eyes, the ocellar mound being on the apex. The posterior portion of the head is strongly depressed in all specimens, rising abruptly to the upturned lateral borders, and gradually from the base forward. A thickened filiform border bounds the lateral margins and a narrow, flat, depressed border the posterior margin. The projecting frontal margin is flat or slightly elevated.
A very striking feature of the carapace is the pearllike projecting eyes placed very far forward and intramarginal, lying in the pit of the concave curve of the lateral margin. The visual surface is distinctly seen in several specimens [pl. 36, figs. 3, 4, 8]. It is crescent shaped and narrow. The ocellar mound which is situated on a line connecting the posterior extremities of the compound eyes is, like the latter, characterized by extreme prominence, and besides by its remarkably large relative size.
Only one specimen has been found that can give a clue to the original form of the abdomen. Corresponding to the diverging lateral margins of the head and its broad basis, this is also broad and widens much toward the posterior portion of the preabdomen, after which it probably contracted rapidly to the telson.
The boundaries of the tergites are but very faintly seen and it is possible that the specimen has suffered contraction by pressure.
The postabdomen and telson have not been seen in place but a curved telson with attached last postabdominal joint [pl. 36, fig. 7] has been referred here provisionally, partly because it could not be placed with any other species and partly because the head and abdomen of E. ? cicerops suggest its reference to Eusarcus and this telson points also to the same genus. Indeed, we consider the presence of this telson good evidence
