280 
Proceedings of the Royal Society of Edinburgh. [Sess. 
Chiridotea entomon, for access to a dried disarticulated specimen of which 
in the Royal Scottish Museum I have to thank Dr James Ritchie : the 
“tergal alae ” described by Lloyd (1908) in the cephalosome of Bathynomns 
likewise come under the category. In all these cases, however, a medial 
girder is absent, while the inturnings are not solidly planted upon the 
cephalosomic floor as in Glyptonotus. 
The Ventral Skeleton. — Curiously enough, when the oral appendages, 
are removed from the cephalosome, the articular foramina for the mandibles 
appear to be directly continuous with the row of articular foramina for the 
perseopods and gnathopods — see fig. 15. As if they did not belong to the 
Fig. 15. — Ventral aspect of the “ cephalosome” of Glyptonotus after removal 
of the appendages. Photograph. Natural size. 
The articular foramina for the pair of mandibles and also for the first 
pair of gnathopods are large and widely spaced, those for the first maxillse, 
the second maxillte, and the maxillipeds being increasingly approximated 
towards the middle line. 
series, the articular foramina for the maxillipeds and for the first and 
second maxillae are medially clustered together, and are borne by a special 
skeletal framework — the maxillo- sternal framework — which is movably 
connected with the buccal frame formed by the main or heavy skeleton of 
the cephalosomic floor. From a purely mechanical point of view this last 
feature of the construction of parts might suggest an analogy with the 
oral region of one of the higher vertebrates, in which the hyoid skeleton, 
light, delicate, and of secondary mechanical importance, has become inclosed 
within the angle formed by the mandibula and tends to relinquish its 
bony union with the cranium (according to this comparison the maxillse 
and maxillipeds of the isopod would correspond to the tongue of the 
vertebrate). 
The articular foramina for the first pair of gnathopods are widely 
