300 ERYLUS ROTUNDUS. 



DIMENSIONS AND SHAPES OF MICRORHABDS. 



Erylus rotundus 



Mitrorliabds 



var. megarhabda 



var. typica 



var. 

 cidaris 



limits and means of averages of all 

 the forms of the species 



A 



B 



limits and means of averages of 

 all the forms of the variety 



A 



B 



C 



D 



limits and means of averages of 

 , all the forms of the variety 



South Molokai 



Kauai 



South Molokai 



Kauai, dark .specimen 



Kauai, hght specimen 



Northeast Hawaii 



Length 



hmits, /( 



45-98 



43-86 



43-98 



35-60 



30-55 



31-58 



46-66 



30-66 



32-55 



30-98 



average of the 

 longest three, /t 



95.7 



82.3 



89 



57.7 



54 



57 



61.7 



57.6 



54 



66.1 



Tliickness 



Hmits, /! 



3-7.5 



3-5.5 



3-7.5 



1.5-3.3 



1.5-3 



2.,5-4 



2-3.5 



1.5-4 



2-4.5 



1.5-7.5 



average of the 

 thickest three, /i 



6.7 



5.3 



6 



3.1 



3 



3.8 



3.3 



3.3 



4 



4.2 



Shape 



gradually and sharply pointed ; central 

 tyle small or absent. 



gradually and sharply pointed; usu- 

 ally without central tyle; this when 

 present, small. 



gradually and sharply pointed; cen- 

 tral tyle small or, more frequently, 

 absent. 



rather abruptly and bluntly pointed; 

 centrotyle. 



sharply pointed; centrotyle. 



abruptly sharply pointed; centrotyle. 



gradually and sharply pointed; usually 

 without "central tyle. 



variously pointed or blunt; central 

 tyle in most, but not in all specimens 

 well developed. 



gradually and sharply pointed; more 

 or less centrotyle. 



variously pointed, with or without 

 central tyle. 



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

 some plagiotriaenes. The rhabdome is conical and generally slightly and irreg- 

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

 cladomal end, 6-12 fi thick. The clades of the same cladome are fairly equal in 

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

 the cladome is 155-440 p.. The triaenes of var. cidaris have the 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 branch-ray or abruptly 

 bent down near the end. 



