CRINOIDEA AND ECHINOIDEA 



35 



Florida : The Tortugas, Sand Key. 5 specimens. 

 *'West Indies." 7 specimens. 



Echinometra viridis 



A. Agassiz, 1863. BulL M. C. Z., /, p. 22. 1872. Rev. Ech., pi. Xa, fig. 1, 



It is unfortunate that Mr. Agassiz 's figure represents the less 

 common thick-spined vanety of this rather uncommon species. 

 On the reefs at the Tortugas, the differences between viridis and 

 Uicunier are very marked and no collector familiar with sea- 

 urchins would confuse them. But after the colors have become 

 dull and faded, the differences are less marked and in photo- 

 graphs the two species might easily be mixed. In the number 

 of pore-pairs in an arc however, the two are constantly differ- 

 ent and in photographs as good as those on plate X a of the Re- 

 vision this difference is easily seen with a lens. In life, viridis 

 is light brown, usually with a yellowish tinge but not uncom- 

 monly reddish; the primary spines are pale brownish at base, 

 rapidly becoming greenish and quite evidently green distally, 

 but tipped rather abruptly with bright purple; the very tip of 

 the spine is sometimes whitish in marked contrast to the purple ; 

 the milled ring at the base of the spine is conspicuously white. 

 The largest specimen of viridis I have seen is 42 mm. long and 

 36 mm. wide; it is the stout-spined form, the primaries being 

 only 18 mm. long and fully 2 mm. thick while in the usual form, 

 spines 18-20 mm. long are only about 1 mm. thick. At the 

 ambitus, there are 5 pore-pairs in an arc, but below, there are 

 only 4; abactinally, clear to the ocular plate, there are but 5 

 pairs in each arc. This arrangement of pore-pairs is characteris- 

 tic of the species and is well shown in much smaller specimens. In 

 E. lucunter, on the contrary, the full number of pore-pairs is 

 6 and if (in a small individual) there are only 5 pairs at the 

 ambitus, some of those above the midzone will show the charac- 

 teristic 6. There is only one specimen of viridis in the Iowa 

 collection and it was taken at the Tortugas. The species is 

 known only from Florida, Jamaica and Hayti. I did not find 

 it at Tobago in 1916, although particular search was made 

 for it. 



