20 IOWA STUDIES IN NATURAL HISTORY 



c- there are iio modified eolumnals, and no cirri; at the end of the 

 stem there is a cluster of roots, or radicular cirri, which may 

 extend upward over a number of eolumnals 

 di the third, sixth and ninth brachials (the fifth, eighth and 

 eleventh ossicles beyond the radials) have a muscular articu- 

 lation at either end ; the basals are fused into a solid ring 

 which is broader than long, cylindrical or truncated conical 



Bathycrinus 



d- all the ossicles following the radials are united in pairs by 

 non-muscular articulations; that is, muscular and non-mus- 

 cular articulations regularly alternate throughout the arm; 

 the basals are separated, or fused into a solid ring which is 

 truncated conical, longer than broad 

 el ten arms (twelve arms in six-rayed species) 



Monaclwcrinus 

 e2 five arms 



f 1 no sutures visible between the basals, which are fused 

 into a solid conical ossicle; four to seven rays 



Ehizocrinus 



t- basals always separated by distinct sutures; always 

 five rays 



gi stem relatively slender, the longest eolumnals at 

 least twice as long as broad; calyx more or less 

 conical 



Bythocrinus 



g2 stem stout, the longest eolumnals rarely so much 

 as twice as long as broad, usually only slightly 

 longer than broad; calyx almost or quite cylin- 

 drical 



Democrinus 



THE PLANT-LIKE INTERRELATIONSHIPS OF THE 

 CARIBBEAN CRINOIDS 



Some years ago I stated that the study of the fixed and seden- 

 tary marine animals was often rendered exceptionally difficult 

 through the more or less complete assumption of that type of 

 variation which we find among the plants. Individuals of many 

 species of plants vary very widely according to the dampness or 

 dryness, richness or barrenness, and brightness or darkness of 

 the locality inhabited, while in other types which will grow only 

 within a relatively small range of conditions the variation is 

 slight. 



