18 G. 0. Sårs. 



the female sex, and closely agreeing as to the animal, 

 whereas the shell is of somewhat different form, being com- 

 paratively shorter in the one specimen (not figured in the 

 plate) in proportion to the height, and more abruptly trun- 

 cated in front. I regard this specimen as a somewhat ab- 

 normally developed individual, and think that the other spe- 

 cimen will give a more correct idea of the species. In both 

 specimens the shell exhibits a rather broad and distinctly 

 defined apposed marginal area, showing that the specimens 

 are comparatively very old, and have probably reached their 

 maximum size. The species is named in honour of Prof. 

 J. R. Henderson, to whom I am indebted for the interesting 

 Phyllopoda treated of in the present paper. 



Description of the female. 



The shell of the larger of the 2 specimens measures 

 14 mm. in length, with a height of about 8 mm. This form 

 is accordingly of very large size, being scarcely surpassed 

 by any of the previously known Estheriidæ. 



Seen laterally (fig. 1), the shell exhibits a somewhat ir- 

 regular oval or elliptic form, in the other specimen almost 

 approaching the trigonal shape. In both specimens the 

 height of the shell exceeds half the length, but more so in 

 the one than in the other specimen (that here figured). The 

 dorsal margin is only straight in the middle; but both an- 

 teriorly and posteriorly it curves downwards, joining the 

 free edges of the valves without any intervening angle. The 

 ventral margin is but slightly curved, and exhibits in the 

 middle a slight insinuation, which, however, in the other spe- 

 cimen was less distinct. The anterior extremity, in the spe- 

 cimen here figured, is somewhat irregularly rounded; in the 

 other specimen it is considerably shorter and more abruptly 



