IONE. 253 
The species are parasites on some of the most curious 
genera of macrourous Decapoda, the British species in- 
festing our only species of Callianassa. 
The only specimen of this genus that we have had an 
opportunity of examining was found on a Callianassa 
taken by Mr. Lord in British Columbia. It was very 
much larger than our British species, and is described as 
Tone cornutus by Mr. Spence Bate in the “ Proceedings 
of the Zoological Society” for 1864. 
The large size of the animal enabled us to examine 
the detail of its structure with comparative ease. Laden 
as it was with mature larve, the large ovigerous plates 
covered the whole of the under surface except the pleon. 
We saw nothing of the delicate narrow membranous 
appendages attached to the legs that Professor M. Edwards 
supposes to be branchiz, like those of the Amphipoda. 
The organs of the mouth consist of several appendages 
much differentiated, and co-operating together so as to 
form one large oval mass, that was evidently endowed 
with some degree of propulsive movement. 
The mandibles consist of a pair of long narrow plates 
that are serrated at the anterior edge, one being obliquely 
convex, the other concave: the one that is concave being 
convex nearer the base, while the reverse is the form of 
the other, so that the blades being each a little curved, 
the two meet at. the point much in the form of a screw. 
These cutting appendages are planted at the extremity 
of the cesophagus, which, from its membranous character, 
probably has a contractile power. 
The two pairs of maxilla appear to be developed 
round the mandibles as a strong support and frame- 
work, the whole of which has the power of being 
pushed out or withdrawn by the assistance of powerful 
muscles that are attached to a strong osseous tendon 
