300 ERYLUS ROTUXDUS. 



DIMENSIONS AND SHAPES OF MICRORHABDS. 



Most of the triaenes (Plate 6, figs. 1-5; Plate 6, fig. 27a) are orthotriaenes, 

 some plagiotriaenes. The rhabdome is conical and genei-ally slighth' and irreg- 

 ularly curved in an undulating manner. It is 170-370 /< long and, at the 

 cladomal end, 6-12 /( thick. The clades of the same dadome are fairly equal in 

 length. They are usually slightly curved and 80-270 /t long. The breadth of 

 the cladome is 155-440 //.. The triaenes of var. cidaria have tlie broadest, those 

 of var. megarhabda the narrowest cladomes. The angle enclosed between the 

 clades and the rhabdome is 90-107°. In form A of var. megarhabda I have 

 found a few triaenes with clades either bearing a small brancli-ray or abruptly 

 bent dowTi near the end. 



