CRINOIDEA AND ECHINOIDEA 



33 



primary spines above the ambitus is distinctly pink and most of 

 the larger primaries have one or two bands of brownish-pink at 

 the middle or distally; these bands are however very faint and 

 might easily pass unnoticed. 



This species and the preceding are so easily confused with 

 the young of Echinus, Lytechinus and even Tripneustes that 

 the following key will be useful to those who have occsaion to 

 sort small West Indian echini. It is based largely upon the 

 material before me in the Iowa collection. 



Buccal membrane thin and perfectly naked or at 



most with widely scattered calcareous granules, 



in addition to the five pairs of buccal plates. 



Periproct covered almost wholly by the huge 

 suranal plate; ocular plates all exsert; gen- 

 eral tint of coloration greenish Genocidaris maculata 



Periproct with many small plates and no con- 

 spicuous suranal; ocular I insert; genera] 



tint pinkish or pure white ..Tripneustes esculentus 



Buccal membrane usually heavily plated or at least 

 with numerous plates in addition to the buccal 

 plates 



Abactinal system large (about .40 test diame- 

 ter), flat, smooth and shining; ocular plates 

 equally exsert; periproct covered by 4 plates, 

 the suranal distinctly largest; test depressed 



and usually more or less sculptured Trigonocidaris aliida 



Abactinal system smaller (.30-.35 test diame- 

 ter), not flat, smooth and shining; ocular I 

 often nearly or quite insert; periproct with 

 6 or more plates; test not depressed and 

 never sculptured. 



Buccal membrane not heavily plated but 



with numerous small thin plates; green 



color in ambulacra abaetinally, confined to 



inner side of the series of primary tubercles. 



the whole inner end of each plate being 



more or less green; ocular I never insert EcMnus gracilis 



Buccal membrane heavily plated; ocular I 

 often insert or more nearly so than the 

 others. 



Test white and light yellow-green, the 

 green color in ambulacra abaetinally, con- 

 fined to outer side of the series of pri- 

 mary tubercles Lytechinus euerces 



Test white and green, but the color in 

 ambulacra occupies more or less nearly 



all the plates Lytechinus variegatus 



Test pinkish or pale brown, with no in- 

 dications of green Lytechinus variegatus ccroUnus 



