OF DECAPOD CRUSTACEA. 53 



After stating in a very clear manner the facts he had established, 

 the author draws the following conclusions. The carapax of the Bra- 

 chyura includes : 



I. The first and second normal segments represented by the epistome, 



or its anterior position, and the inter-antennary septum. 



II. The third normal segment, represented by the main body of the 



carapax, and the anterior portion of the prelabial plate or pal- 

 ate. 



III. The fourth normal or mandibular segment represented by the 



posterior and outer part of the prelabial plate and the ventral 

 pieces of the carapax. 



Concerning the carapax of the Macroura the author again 

 differs from Milne-Edwards in designating the lateral and 

 posterior plates of the carapax of Astacus mandibular terga 

 instead of epimera. After a careful comparative descrip- 

 tion of numerous forms both among the Macroura and the 

 lower Crustacea (loc. cit., pp. 32-37) in which he men- 

 tions several seemingly adverse cases, the author concludes 

 that the origin of the carapax and the disposition of its 

 parts are essentially the same throughout the class. 



From the foregoing extracts it will be seen that Dana's 

 views are in advance of those of the other investigators, 

 but there yet remain several points of interest on which 

 it is desirable to collect further evidence. Both Milne- 

 Edwards and Dana have established with a high degree of 

 probability the origin of the carapax from the terga of the 

 mandibulary and antennary somites, but neither of them 

 succeeded in finding a conclusive demonstration of the 

 fact. In the very young Squilla the thoracic and ab- 

 dominal segments of the body may, by careful dissection, 

 be removed from their connection with the carapax, with- 

 out disturbing the relation of the parts in intimate connex 

 with the latter. In such a preparation the point of attach- 

 ment will be seen to lie immediately behind the mandibu- 

 lary sternum, fig. 15, z. Since both the ophthalmic and 

 the antennulary segments are entire and have no connection 



