OF DECAPOD CRUSTACEA. 55 



In Cancer, tig. 3, the connection of the ophthalmic 

 with the antcnnuhiry sternum is still closer and the former 

 is a much thinner plate. In /Sci/IIa, tig. 9, the rostrum is 

 hardly in contact with the ophthalmic sternum, although 

 it is hent down close over it. The suture between the 

 ophthalmic and antennary sterna is obliterated. In Plaly- 

 onychusy fig. 1, the fusion between the two sterna is com- 

 plete. In Palinui-us, figs. 14 and 16, Liihodes, fig. 11, 

 and Homarus, fig. 5, the rostrum has not encroached up- 

 on the ophthalmic somite and the sternum sustains its nor- 

 mal relations to the apjiendages. 



Antennulary sternum. The antennulary sternum 

 in Actoeodes is an elongated, bar-shaped plate extending 

 across the facial area immediately below the antennae. 

 The antenuules abut upon its ends, while the ophthalmic 

 sternum is fused to its upper part dividing it into halves. 

 The figure formed by these two plates is that of a short- 

 stemmed T inverted. This plate forms the floor of the 

 antennary sockets. The suture between the antennulary 

 and the antennary sterna is lenticular in form and occu- 

 pied by a semicalcified membrane. 



In Cancel' f fig. 3 and Platyonychus, fig. 1, the parts in- 

 cluded in the facial area are much less distinct. In Scylla, 

 fig. 9, this sternal plate lies opposed to the upper margin 

 (surface) of the antennary sternum, in the form of a 

 thin calcareous plate. Its relations to the surroundin<y 

 parts are, however, the same as in Actoeodes. In Liihodes, 

 fig. 11, the antennulary sternum resembles in all respects 

 the ophthalmic, and consists of a smooth, scarcely calci- 

 fied membrane stretched between the antenuules. In 

 Palinurus, figs. 14 and 16, the antennulary sternum is 

 enormously enlarged and projects forward in the form of 

 a truncated pyramid, equivalent to the "nasal region" of 

 Milne-Edwards. Owing to the unusually large size 



