AND DISTRIBUTION OF TRILOBITES. 261 
find generic peculiarities prominently exposed in these sutures. 
Wahlenberg certainly has already fully appreciated the importance 
of one of these sutures, the so-called facial suture; and Dalman 
and Boeck have subsequently followed in his steps; but it has by 
no means been appreciated by all paleontologists as it deserves. 
For this reason it will not appear superfluous to enter somewhat 
more particularly upon the consideration of these peculiar su- 
tures. In the Dudley Trilobite, Calymene Blumenbachii (Buck- 
land’s ‘Geology,’ 46, 2), we observe, even on a mere superficial 
inspection, two generally indented lines, which proceed from the 
angle in a curved course diagonally over the lateral portions of 
the cephalic shield, and meet at the anterior margin in an arch 
coming from both sides ; the cephalic shield is frequently divided 
by them into three different pieces. 
This composition of the upper covering of the cephalic shield 
of three pieces, which are connected in the above-mentioned 
lines, but which are nevertheless capable of being separated from 
one another, has been met with in almost all Trilobites; the 
only genera in which it is not known to occur are Ampyx and 
Arges. Corresponding with these parts, the forehead part and 
the two maxillary pieces, we find on the under surface likewise 
three (rarely two ?) pieces united by sutures in the same manner, 
leaving open the central part which is situated beneath the fore- 
head part, as we observe in the axis of the thorax and caudal 
shield; here the masticatory apparatus was situated, of which 
however not a trace is met with, with the sole exception of the 
labrum, resembling that of Apus cancriformis. Of the pieces 
of the lower side, the lateral ones are situated beneath the cheeks, 
and only separated from them by a narrow cavity; the third 
odd piece forms the lower part of the anterior margin and bears 
the labrum posteriorly, which itself again consists of a hori- 
zontal part, two-pointed at the extremity, and of two wing-like 
ascending appendages, which are affixed on each side in the su- 
ture between forehead and cheek *. Of all these pieces and 
sutures only those of the upper surface are valuable for our pur- 
pose, since those of the under surface are too rarely accessible 
to observation. The suture in which the pieces of the upper and 
lower covering of the head meet is equally of as little value ; 
* This apparatus, which was first observed by Stokes, was most carefully in- 
vestigated by Pander, who however was less successful in the interpretation of 
the parts. (Pander, Contributions to the Geology of Russia, Petersburg, 1830.) 
