78 THE DIFFERENCES BETWEEN 
of its area, is occupied by a dusky spot with short rays of 
this color reaching out along the sutures between adjacent 
plates. This dusky area is closely lined with obscure pale 
stripes. 
The head of ilf . geograpldcua shows a mark l)ehindeach 
eye comparable to that I have descriI)Gd for M. lesueiiri. 
It is never comma-shaped and is generally, perhaps al- 
ways, completely isolated. It may be circular in outline, 
but is more olten triangular, elongated and placed longi- 
tudinally on the head. It is very commonly enclosed b}^ 
a very faint pale line from which another narrow line ex- 
tends backw^ard upon the neck. A median line occurs 
here also. It extends posteriorly from the snout, gradu- 
ally widening to its posterior extremity, which is on a line 
with or a little anterior to the anterior edges of the spots 
behind the eyes. On each side of this line is a couple of 
faint lines which in some cases turn inwards behind the 
median line where corresponding lines unite. In other 
cases the inner lines unite thus, while the two outer join 
to form a single median stripe which continues posteriorly 
upon the neck. The characteristic line of the side of the 
head is a rather wide one which originates on the tympa- 
num and thence extends ventrally and posteriorly u})on 
the neck. Sometimes it gives off a spur towards the an- 
gle of the mouth and still another at the ventral edge of 
the mandible. A small pale dot is commonly visiljle be- 
neath each eye. Spots corresponding to those described 
as on the mandible near the angle of the mouth in the other 
species can be made out here. But instead of the .spot on 
the symphysis is a median line which extends to the pos- 
terior edge of the mandible where it expands and divides 
into two lines which diver2;e backwards on the ventral side 
of the neck. The expanded posterior ends of the ridges 
of the dorsal plates are brownish-black in young, but not 
