184 EVENINGS AT THE MICK0SCOPE. 



adult need hardly be pointed out any farther than by re- 

 ferring to the figure. When they first escape they rarely 

 exceed half a line in length. The body is ovoid, the 

 dorsal shield large and inflated; on its upper edge and 

 about the middle is a long spine, curved posteriorly, and 

 rather longer than the diameter of the body, though it 

 varies in length in different specimens ; it is hollow, and 

 the blood may be seen circulating through it. The upper 

 portion of the body is sap-green, and the lower semi- 

 transparent. The eyes are large, sessile, and situated in 

 front, and the circumference of the pupil is marked with 

 radiating lines. The lower margin of the shield is waved, 

 and at its posterior and lateral margin is a pair of nata- 

 tory feet. The tail is extended, longer than the diameter 

 of the shield ; and is composed of five equal annulations, 

 besides the terminal one ; its extremity is forked, and the 

 external angles are long, slender, pointed, and attached to 

 the last annulation by joints. Between the external angles 

 and on each side of the median line are three lesser spines, 

 also attached to the last ring by joints. Between the eyes, 

 and from near the edge of the shield, hangs a long, stout, 

 and somewhat compressed appendage, which, as the 

 animal moves, is reflexed posteriorly between the claws. 

 Under each eye is another appendage, shorter and slightly 

 more compressed. The claws are in three pairs ; each is 

 composed of three joints, and terminates in four long, 

 slender, hair-like appendages. These claws are generally 

 bent on the body, but stand in relief from it. If the 

 animal be viewed in front, the lower margin of the dorsal 

 shield will be found to be waved into three semi-circular 

 festoons, the two external of which are occupied by the 

 eyes, and between which the middle one intervenes ; the 

 general direction of the claws will be seen to be at right 

 angles to the body. As the young lies inclosed within the 

 membranes of the egg, the claws are folded on each other, 

 and the tail is flexed on them so far as the margin of the 



