50 



SIDONOPS BICOLOR. 

 DIMENSIONS OF STOUT AMPHIOXES. 



The slender amphioxes (Plate 9, figs. 7, 8) are curved in a simple (Fig. 7) 

 or wavy (Fig. 8) manner, cylindrical in the central parts, and attenuated to fine 

 points at the ends. They are 3.5-9 mm. long and 15-40 ft thick. The longest 

 measuretl were from specimens from Stations 4531 and' 4551, but as the long ones 

 are usually broken in the spicule-preparations it is probable that slender amphi- 

 oxes, considerably longer than those observed and measured, occur also in the 

 specimens from tlie other stations. 



DIMENSIONS OF SLENDER AMPHIOXES. 



The exceedingly rare styles, whicli I observed only in the si)ecimens from 

 Station 4551, are a little over 4 mm. long and at the somewhat thickened rounded 

 end 100-120 // thick. 



The plagiotriaenes (Plate 9, figs. 1-6, 12-14) generally have a straight 

 conical rhabdome, rather abruptly attenuated at the acladomal end and 

 pointed (Plate 9, figs. 13, 14). The rhabdome, when thus normally de- 

 veloped, is 2.1-4 mm. long and at the cladomal end 62-110 u thick. Just 

 below the cladomal end it is markedly thickened and here attains a transverse 

 diameter of 73-120 /<. This thickest part of the rhabdome is 5-20, most fre- 

 quently about 11 % thicker than the cladomal end, which consequently appears 

 constricted in a neck-shajied manner. In some plagiotriaenes the rhabdome 

 is reduced in length, more cylindrical in shape, and simply rounded off at the 

 acladomal end (Plate 9, fig. 12). Occasionally tliis reduction goes so far that 

 the rhabdome measures only 290 n in length. Such very short rhabdomes are 

 cylindrical and not constricted at the cladomal end. They have been observed 

 only in a specimen from Station 4420 and here also they are rare. The clades 

 are conical, quite blunt, and fairly straight (Plate 9, figs. 1, 3-6, 12) or 



