524 THE AMEBIC AN NATURALIST [Vol. XLIX 



the posterior opening of the spiral digestive tube, gives 

 the only visible indication of a departure from true pen- 

 tamerous symmetry. 



In certain types, however, a more or less marked devia- 

 tion from the characteristic symmetry occurs. This devi- 

 ation follows four different lines : 



1. A rearrangement of the five primary groove trunks 

 upon the disk whereby (a) the left posterior increases in 

 size and gives off more branches than any of the others ; 

 (b) as a result of the anterior migration of the mouth, 

 the two posterior become much longer and the anterior 

 much shorter than the others and a condition of bilateral 

 symmetry is attained; (c) correlated with the anterior 

 migration of the mouth, all of the primary groove trunks 

 become merged into a horse-shoe shaped ring which 

 skirts the lateral and anterior borders of the disk, giving 

 off branches to the arms, the mouth being in the right 

 center of the ring so that the ambulacra on the left are 

 more developed than those on the right, or the ambulacra 

 leading to the left posterior arm disappearing altogether 

 so that the ambulacra on the right are more developed 

 than those on the left ; 



2. A dwarfing, or an overdevelopment, of the left poste- 

 rior, more rarely of both, posterior radials with their 

 post-radial series; 



3. The intercalation of additional radials and post- 

 radial series which alternate with the original five, and 

 the associated dropping out of one of the five radials ; and 



4. The suppression of two of the primarily five basals. 



The Asymmetkicai, Ckinoids 

 In the following list are given all the families and 

 genera of recent crinoids which include asymmetrical 

 species. 



After the families the bathymetrical and thermal 

 ranges are given, and after the genera the bathymetrical 

 range. 



Certain families are represented in the warm littoral 



