284 
Proceedings of the Royal Society of Edinburgh. [Sess. 
ventral destination the fold or reduplication, which in the last paragraph 
but one was shown to represent the lateral part of the first thoracic tergite, 
we discover that, after curving round the medial free edge of the first 
triangular lamina near the floor of the cephalosome (see fig. 16), it ends 
in the styloid calcification. 
The position of the styloid calcification therefore corresponds with the 
ventral termination of the first thoracic tergite. Whether it is exclusively 
formed by the first thoracic somite cannot be said : it is possible (though 
Fig. 17. — Diagrammatic horizontal section through the “cephalosome” of 
Glyptonotus. To show the relation of parts near the lateral ceplialo-thoracic 
cleft. 
A, mandibular somite ; B, cephalo-thoracic cleft ; C, second thoracic 
somite ; X, first triangular lamina ; Y, first thoracic somite, rudimentary 
and confined to the bottom of the cephalo-thoracic cleft ; Z, second triangular 
lamina, belonging to second thoracic somite. 
on the whole improbable) that maxillary somitic elements likewise enter 
into its composition. 
While the posterior limits of the mandibular somite of the cephalon can 
be successfully traced in parts, it is a striking fact that no element in the 
roof or side-wall of the cephalosome can be identified as belonging to the 
maxillary somites. In the interior of the cephalon there are calcified 
structures of undetermined origin (see under Ventral Endophragmal 
Skeleton) which are directly connected to maxillary sternites, but these 
are far removed from the roof and lie ventral to the gut. 
One might also call attention to the fact that whereas in Glyptonotus 
the first and second thoracic somites have fused together, in Ghiridotea 
entomon, Harger, the articulation between these two somites is movable. 
The Maxillo- sternal Framework has a longitudinal axis composed of a 
