34 



NATURAL HISTORY BULLETIN 



Some of the differences in the above key may seem trivial but 

 they are surprisingly constant. Of course there are additional 

 and often much more important differences than those here 

 given; these are selected because they are so easily seen. The 

 most common confusion is between Trigonocidaris and Lyte- 

 chinus euerces and specimens of equal size, especially if under 

 10 mm. in diameter are often hard to distinguish. But the 

 flattened and sculptured test of Trigonocidaris, with its large 

 shiny abactinal system and 4 periproctal plates are generally 

 distinctive. There may be added however, as additional fea- 

 tures, the lack of any distinct green in the coloration and the 

 fact that the white actinal spines are commonly encircled with 

 a broad red band. Very small specimens of euerces have no 

 green in the coloration but there is little or no red on the actinal 

 spines. The pretty coloration of Echinus gracilis is very dis- 

 tinctive even in young specimens. Probably Genocidaris is the 

 most easily recognized of the small echini; the huge suranal 

 plate, together with the distinctive coloration, the test-sculpture 

 and the naked buccal membrane, make it a well-marked form. 

 The specimens of Genocidaris in the Iowa collection are from 

 the following places: 



Station 27. Florida : southeast of Sand Key Light, 50-60 fms. 



1 specimen. 



Station 48. Florida: southeast of Key West Light, about 



80 fms. 1 specimen. 

 Locality unkno^^Ti. 112 specimens. 



Echinometra lucunter 



Echinus lucuntei- Linnl, 1758. Sys. Nat. ed. 10, p. 665. 



Echinometra sulangularis A Agassiz, 1872. R^v. Ech., p. 283, pi. Xa, figs. 



2 4. 



Echinometra lucunter Lov6n, 1887. Ech. Linnseus, p. 157. 



This very common sea-urchin is only mentioned twice in the 

 "Narrative", where it is spoken of as being found at the Tor- 

 tugas (p. 133) and on Pourtales Plateau (p. 174) in shallow 

 water. The specimens before me are from the following places : 



Bahamas : Eleuthera, Harbor Island, 1 specimen. 



Bahamas: Little Cat Island. 1 specimen. 



