LIMULUS AN ARACHNID. 627 
Lastly, in regard to that element of the sternum which in 
Buthus is the pentagonal “thoracic metasternite,” and in 
Limulus forms the “chilaria” or paired metastoma, the 
Kurypterinesserve to tie Limulus more tightly to the Scorpion. 
The duplicate character of the chilaria of Limulus renders 
it at first difficult to admit that they are represented by a 
single median plate in Scorpio. This right-and-left cha- 
racter even led M. Alphonse Milne-Edwards to ignore the 
position of the genital apertures and to identify the chilaria 
of Limulus with the pectens of Scorpio. The Eurypterines 
show clearly enough (evenin the absence of embryological 
evidence) the sternal nature of the King Crab’s chilaria, 
for they possess, just where thechilariaof Limulus are found, 
a single broad oval plate, which rises up from the surface in 
such a way as partly to cover in and work as lower lip to 
the four pairs of coxal jaws in front of it (see woodcut, fig. 
19 ch). This single metastoma, or chilarium,is readily under- 
stood also as the equivalent of the single pentagonal sternite 
of Scorpio, which is dwindled in size and pushed away in 
that animal from the functional jaws by the large ankylosed 
coxe of the fifth and sixth pairs of cephalothoracic appen- 
dages. 
D. Review oF Opinions oF MopERN AUTHORITIES AS TO 
THE AFFINITIES OF LIMULUS. 
So far in preceding pages my object has been to point out 
definite points of special resemblance between Limulus and 
Arachnids, especially the Scorpion. I have not paused to 
insist upon the absence of any such special agreements 
between Limulus and the Crustacea. I propose briefly to 
do this now by examining the statements of those who have 
asserted that any such special agreements exist. 
Clearly between Limulus and any other Arthropod there 
must exist agreements which are the common characters, 
more or less, of all Arthropods. It may also be possible to 
find structural features which are exhibited only by Limulus 
and by Crustaceans, one feature finding its parallel in one 
Crustacean and one in another. But I think it must be 
definitely conceded (1st) that there is no one Arthropod in 
which anything like so large a number of the structural 
features found in Limulus are paralleled as the Scorpion, and 
(2nd) that there are several structural features exhibited by 
Limulus which have no parallel in the Crustacea at all, but 
are common to Limulus and the higher Arachnida. 
Putting together Limulus and the Eurypterines we may 
