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 

 lone 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 larvae, 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 branchiae, 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 oesophagus, which, from its membranous character, 

 probably has a contractile power. 



The two pairs of maxillae 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 pushed out or withdrawn by the assistance of powerful 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 



