78 HAWAIIAN AND OTHER PACIFIC ECHINI. 



Rotula. 



Agassiz, 1841. Mon. Scut., p. 23. 

 Type, Rotula rumphii Agassiz, I. c. = Echinus orbiculus Linne, 1753. Sys., Nat. ed. 10, p. 666. 



Unfortunately I have been unable to examine any specimens of this genus 

 except bare tests. One of these shows parts of the buccal membrane which 

 seems to have been heavily plated, a most unusual condition in clypeastroids. 

 The spines and pedicellariae will no doubt show some interesting peculiarities. 

 The number of species in the genus is still uncertain, for while I can distinguish 

 only the two which have long been known, Rochebrune (1881, Nouv. Arch. Mus. 

 Paris, ser. 2, 4, p. 328, pi. 19) figures two very different forms which he considers 

 separate species, neither of which has lunules. Moreover none of the specimens 

 examined have oval, nearly closed petals as in his figures, but always narrow, 

 widely open petals with poriferous areas nearly parallel. Whether his figures 

 err, or whether the form of the petals is very variable, or whether he is really 

 dealing with species different from any I have seen, I am unable to decide. 



Key to the Species of Rotula. 



Test without lunules orbiculus. 



Test with a lunule in each anterior interambulacrum deciesdigitata. 



Rotula orbiculus. 



Echinus orbiculus Linne, 1758. Sys. Nat., ed. 10, p. 666, no. 17a. 



Rotula orbiculus Meissner, 1904. Bronn's Thier-reichs, 2, abt. 3, buch 4, p. 13S4. 



Rotula rumphii Agassiz, 1841. Mon. Scut., p. 25. A. Agassiz, 1S72. Rev. Ech., pt. 1. p. 155 



This species is known from Senegal and the Cape Verde Islands. 



Rotula deciesdigitata, comb. qov. 



Echinodiscus deciosdigitatus Leake, 1778. Add. ad Klein, p. 1 15. 



Rotula augusti Agassiz, 1841. Mon. Scut., p. 28. A. Agassiz, L872. K . Ech., pt 1. p. r>l 



This species is known only from Liberia and adjacent African coat 



