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1916-17.] Experiments and Observations on Crustacea. 
lateral) border of the mandibular articular foramen is obviously formed of 
two separate elements, separated by a deep fissure — see fig. 18 . One half, 
the more lateral, is simply a strongly calcified portion of the main latero- 
ventral skeleton of the cephalosome proper. As this part carries the 
posterior of the two bearing surfaces at each end of the axis of the mandi- 
bular hinge, we can be reasonably certain that it is a portion of the 
Fig. 16. — End view of the interior of the “ cephalosome” of Glyptonotus. x 6. To show the alar 
piriform bodies, and the relation of the first to the second triangular lamina. 
a, medial plate-like girder of first septum ; b, cephalo-thoracic foramen ; c, capsule of alar 
piriform body partially lifted behind (this structure is wholly rounded, not concave behind as 
is suggested by the figure) ; d, first triangular lamina (probably belonging to mandibular 
somite) ; e, first thoracic somite ; /, second triangular lamina (belonging to second thoracic 
somite) ; g, foramen for nerve-chain. 
primitive mandibular somite ; which in turn means that the anterior wall 
of the cephalo-thoracic cleft, if not the whole of the first triangular lamina, 
has been formed by the mandibular somite. 
The more medial half of the border of the articular foramen consists 
of a curiously shaped calcification, the styloid calcification , which projects 
ventrally as a styloid process. Though it lies pronouncedly in front of 
the anterior border of the second thoracic sternite, it is welded firmly to 
this sternite, as well as to the mandibular somite. When we trace to its 
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