DECAPODA' 365 



has at the sides (where, as the branchiostegite, it covers the gills), not 

 an arched profile but runs out almost horizontally and is then bent 

 in, at an angle (a.l.e.) which is more acute in the anterior part of the body 

 than in the hinder part, to end against the flank above the coxopodites 

 of the legs. At the angle, the branchiostegite, viewed from above, 

 describes the lateral part of the outline of the body. That outline 

 begins between the eyes, where in the crayfish the rostrum stands, 

 with the front, a low, three-toothed lobe. On each side of this is the 

 orbit y an excavation of the surface of the head for the reception of 



en^ 



Fig. 271. 



Fig. 272. 



Fig. 271. Diagram of a transverse section through a branchial chamber of 

 Carcinus maenas. From Borradaile. a.l.e. anterolateral edge; cp. coxo- 

 podite; eh.sp. epibranchial space; ep.i, epipodite of the first maxilliped; 

 ep. 3, epipodite of the third maxilliped; hy. hypobranchial space; i.r. layer 

 of branchiostegal fold; o.r. outer layer of the same; proc. process of flank of 

 thorax, which meets branchiostegite and separates two of the openings above 

 the legs into the chamber. 



Fig. 272. The left third maxilliped of Astaciis. cp.set. coxopoditic setae; 

 en. endopodite; ep. epipodite; ex. exopodite. 



the eye. From the orbit the notched anterolateral edge curves out- 

 wards and backwards as a crest on the branchiostegite, forming with 

 its fellow and the front a semicircle. From each end of the semicircle 

 a slightly concave posterolateral edge carries the outline slanting 

 inwards to the short, transverse /)05^mor edge of the carapace. 



To return to the transverse section : the thin inner layer of the fold 

 which makes the branchiostegite is not so much drawn out as the 

 stout outer layer, so that a considerable space is left between them. 



