PLATE 81 B. 
Page 
Fig. 1-4. Eurypterus lacustris. 
1. A specimen of medium size, lying with the dorsal side exposed. The carapace has been 
broken off, showing the inner side of the maxillary plates, the post-oral plate, and the 
four anterior pairs of feet, which are obscured at their bases. The body is curved, and 
the tail-spine directed forwards. The pustuliform scales upon the back are in four rows 
on the thoracic joints, and two slightly diverging rows on the abdominal joints. 
2. The last joint of the swimming foot, with the minute palette at the extremity. 
3. The seventh joint of the swimming foot, having the triangular chelate extension separated 
at the suture. 
4. The first articulation of the ventral side, with the organs attached. 
407* 
