Besides the scales and spines the integument of the eurypterids was also in many parts covered with fine hairs as in Limulus, especially on the lips and legs. These have been observed and photographed by Holm in E. fischeri.
Pores of doublures. Schmidt [loc. cit. p. 67] has observed that in Pterygotus the posterior third of the dorsal thoracic segments is provided with a separate interior lamella or doublure ("Umschlag") perforated by numerous fine tubes especially abundant toward the posterior and lateral margins. In Eurypterus this doublure is present but imperforate.
A slightly weathered specimen of Pterygotus buffaloensis very beautifully exhibits this interesting feature not only verifying Schmidt's observations but also allowing some amplification of them. In this specimen, the pores are distributed over the whole lamella, but are most closely arranged and most distinct in a belt occupying the posterior third of the lamella except for the hindmost millimeter which is entirely imperforate. Where fully exposed, they appear as sharp black lines, about 11/2 millimeters long, passing from below and posteriorly, obliquely upward and forward. At the posterior margin of the belt they stand more vertical but they rapidly bend forward and increase in obliquity of direction toward the anterior margin of the belt. They are most distinct on the tergites, but have been seen on the sternites in a similarly situated, though narrower belt, corresponding to the smaller width of the doublure. Similar belts of pores are visible on the posterior thirds of the broad doublures of both the dorsal and ventral sides of the abdominal segments, and on the narrow doublure of the posterior margin of the head.
The weathered head of the same specimen also exhibits anastomosing lines near the center and a ring of several rows of black points and lines which seem to indicate either the presence of similar pores or of a system of pits.
Another row of pits which seem to have been pores, is also seen just inside the flexure of the head shield into the doublure. These would seem to correspond to the row of "Punkte" observed by Holm in Eurypterus
