624 PROFESSOR E. RAY LANKESTER, 
A genital operculum of the same proportions as that of 
Limulus is present, and traces of appendages (sternal plates), 
corresponding to the five pairs of branchial plates of that 
Fic. 19.—Pterygotus Angticus. The segments are numbered to show their 
agreement with those of the Scorpion (see Fig. 2). oc, compound 
eye; ch, chilarium; gez, genital operculum ; az, anus ; PA, post-anal 
spine or plate. 
Fia. 20.—Slimonia acuminata. oc, compound eye, lateral; oc’, simple eye, 
central; PA, post-anal spine. 
animal, have been detected on the following segments. The 
cephalothoracic tergum is, in some Eurypterina, horseshoe 
shaped as in Limulus, though relatively smaller in size, and 
the eyes appear to have been similar to those of Limulus 
in character and position, though the compound eyes are 
close to the margin of the carapace instead of at some distance 
from it. Though in many Eurypterina the cephalothoracic 
appendages are simple tactile or ambulatory organs, yet in 
others we find (as in Pterygotus) the chelate form appearing, 
as with the majority of these limbs in Limulus. 
I am anxious here to point out that there is not only a 
general resemblance of the Eurypterine body to that of the 
Scorpion, but that in many of the most important points in 
which they differ from those of Limulus the Eurypterine 
body and appendages agree precisely with those of the 
Scorpion, and not in a merely general way, The Kuryp- 
