14 



Huxley* in his short account of the crab states that 

 the ophthalmic and antennulary sterna are fused, and 

 that the suture is between the fused sterna and the 

 rostrum. I am of the opinion that the whole of the 

 sternum behind the suture belongs to the antennulary 

 somite alone, and that the septum separating the 

 articular cavities of the optic peduncles is a posterior 

 prolongation of the rostrum, as described above. 

 An examination of the sternum from the dorsal side 

 (PI. Ill, fig. 19) shows that the suture is on a level with 

 the posterior boundary of the ophthalmic articular cavity ; 

 so that, if Huxley's view be accepted, we have the 

 ophthalmic sternum entirely behind the articular cavity 

 of its own somite ! It is much more reasonable to 

 conclude that the suture separates the ophthalmic septum 

 from the antennulary sternum. 



The Epistoma is a broad plate in front of the mouth 

 and immediately behind the first sternum. It represents 

 the united sterna of the second (antennary) (S 2 ) and third 

 (mandibular) ( 3 ) somites. Its anterior border is concave 

 in front. The two lateral borders gradually slope inwards 

 towards their posterior ends. The posterior border is 

 deeply concave behind and bounds the front edge of the 

 mouth. 



The middle part of the anterior border touches the 

 posterior edge of the first sternum and the two outer 

 portions bound the posterior edge of the second antenna. 

 The lateral borders are in contact with the membranous 

 roof of the pre-branchial chamber. 



From the middle of the anterior border of the ventral 

 side of the epistoma a median groove passes backwards 

 but does not extend as far as the posterior border. From 



* T. H. Huxley, Manual of the Anatomy of Im-ertebratecl Animals, 

 1877, pp. 340-345. ' 



