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 in length the remainder of the body. The curved position of the postabdomen in several specimens demonstrates the great flexibility of this part, while the downward curvature of the telson would make it a dangerous weapon when the postabdomen is thrown forward over the body, as this action would bring the tenninal spine into the position of an upturned sharp pointed scimitar.

There is a striking morphological similarity between the telson of Eusarcus and the tail of the scorpion and in view of this and the acknowledged close relationship of the merostomes with the scorpions, it becomes a fair question whether the tail spine may not have been equipped with poison glands. The preservation of the telson is not such as to permit the determination of the presence or absence of apical pores for the emission of the venom, or of the poison canal in the compressed spine. The form of the body of the animal does not suggest great agility, either in walking or swimming, but rather a habit of burrowing in mud or lying in wait for prey. In the absence of powerful prehensile organs of long reach, a quick dispatch of the prey must have been a necessity and this could have been well accomplished by an agile and venomous telson.

The table of measurements shows that the young individual exhibits interesting and probably phylogenetically significant differences from the adult in the general proportions of its body. The most notable of these is the relatively greater width of the preabdomen; for while in the young the proportion of length to width here is as 2 : 3, in the older specimens it is as 4 : 5. The postabdomen also is relatively wider or stouter than in the older individuals, while on the other hand, the relative lengths of preabdomen, postabdomen and telson to the total length have remained nearly the same. Still younger individuals would surely show other differences in these ratios. The cephalothorax which in our young and old individuals occupies about one sixth of the length and is a relatively insignificant part of the body, compared with the other eurypterids, has most probably lost in relative proportion during ontogenetic development.