PLATE 81. 



P»ge 

 Fig. 1 - 11. EURYPTERUS LACUSTRIS. 407* 



1. A young individual, preserving but one of the larger appendages on one side : the poste- 



rior spine is broken off near the distal extremity. 



2. An individnal of medium size, preserving all the articulations of the body, the fourth foot, 



and one of the swimming feet imperfect. 



The specimen lies upon the stone with the back downward, and the crust from the 

 lower side is almost wholly removed, so that the inner sides of all the parts are seen, and 

 the cavities of the eyes. The last joint of the swimming foot is separated at the articula- 

 tion r ; and the suture at the base of the fixed ramus of the chela, which is naturally 

 solid, is slightly separated s. The other joints are somewhat distorted by pressure, which 

 has been directed from below upwards. On the right side of the figure, and on the last 

 articulation, there are small portions of the ventral crust remaining. In this specimen, 

 the interior of the crust being seen, the imbrication of the rings of the body is reversed. 



3. The exterior of a head or carapace of a larger individual, which preserves the eyes. 



4. The two posterior annulations of the body, with the caudal spine attached. The specimen 



lies with the dorsal side downwards; the ventral crust being removed from the annula- 

 tions, and the lower concave side of the spine is shown. 



5. A separated caudal spine, showing the lateral and lower sides. The specimen is much 



compressed. 



6. The ventral side of the body, preserving nine of the segments : the two upper are joined 



by a close suture, and sustain a locomotive [? ] appendage. 



7. The upper thoracic segment separated from the body, and scarcely showing the suture 



line : the articulated appendage is imperfect. 



8. A very large thoracic segment, showing the suture line and the appendage before men- 



tioned, from which the lower articulations are separated. The continuation is drawn from 

 the one shown in fig. 6. 



9. A single articulation of the thorax. The line near the upper margin, including a portion 



which is broken off, indicates the extent of the imbrication of the next superior segment. 



10. A part of a segment which is longitudinally divided ; a feature shown along the dorsal line 



in several articulations in another nearly entire individual. It is probable that this de- 

 hiscence of the rings along the back is connected with the process of casting the crust. 



11 . A portion of the surface of fig. 8 enlarged. 



