226 WALTER GARSTANG. 



second antennse. The scaphognathite is of unusual size ; both 

 in A. symnista and in A. raicrops its anterior edge touches 

 the basal joint of the antennules, while its posterior extremity 

 is level with the base of the second thoracic leg. It is, in fact, 

 half as long as the body (excluding the antennules) in the 

 attitude represented in fig. 4 a. 



In Corystes the roof of the prostomial chamber is largely 

 furnished by the projecting frontal area of that animal 

 (fig. 3a). In Albunea, however, the frontal area is eraargi- 

 nated (fig. 4a), and the roof of the prostomial chamber is 

 furnished by the eye-peduncles, whose flattened scale-like form, 

 varying in shape in the different species, is one of the most 

 characteristic features of the genus (figs. 4 a and 5). 



In Corystes the three stout basal joints of each antenna 

 are disposed at right angles to one another in the vertical 

 plane, bringing about a characteristic bend in the basal part 

 of the antenna (figs. 3a and 3 6), a feature which is functionally 

 correlated with the reversal of the branchial current and its 

 course through the antennal tube. 



A precisely similar arrangement is recognisable in the species 

 of Albunea, but in connection with the antennules instead of 

 the antennse (figs. 4a and 5). In A. symnista (fig. 4a) the 

 joints are disposed at right angles to one another, as in 

 Corystes cassivelaunus ; but in A. scutelloides (fig. 5) 

 the distal joint is pressed much farther back than in either of 

 these forms, thereby greatly reducing the angles of inclination. 

 This difference may be readily seen to be correlated with the 

 fact that in the latter form the part played by the frontal 

 region in covering the prostomial chamber is very much less 

 than in Corystes cassivelaunus or A. symnista. In 

 Corystes the roof is provided by the prominent frontal area 

 (fig. 3a); in A. symnista by the apposed plate-like optic 

 peduncles (fig. 4a), but in A. scutelloides the optic plates 

 are so small and short that they scarcely project from the 

 orbital emarginations. The increased backward bend of the 

 antennules in the latter species compensates for this deficiency. 



In the figure of A. scutelloides (fig. 5) the antennules 



