56 HAWAIIAN AXD OTHER PACIFIC ECHINI. 



from each other by any external characters. Yet the internal structure of the 

 test is so different in the two genera and this difference is so constant, that I have 

 been forced to adopt as the distinguishing character the presence or absence of 

 internal radiating partitions. Comparison of figures 3 and 7 on Plate 126 

 will make this difference more clear than an elaborate description. The parti- 

 tions in Echinocyamus do not always extend the whole length of the radius 

 but may run inward only a short distance from the margin (PI. 127, fig. 3). 

 In Fibularia, however, there is generally no indication of such partitions except 

 in the posterior jjart of the test. Externally the two genera are strikingly 

 similar, especially when covered with their spines, but as a rule the species of 

 Echinocyamus are flat and broad while in Fibularia, the vertical diameter is 

 usually more considerable. Echinocyamus is world-wide in its distribution 

 although it is not yet known from the west coast of America, but Fibularia is 

 confined chiefly to the East Indian region, ranging from Japan to Australia; 

 specimens are also known however from the Red Sea. 



Key to the Genera of Fibulariidae. 



Tost more or less elevated, without internal radiating walls, except posteriorly where 



they are usually indicated Fibularia. 



Test more or less flattened with internal radiating walls bounding the ambulacra . . Echinocyamus 



Fibularia. 



Lamarck, 1S16. Anim. sans Vert., 3, p. 16. 

 T\'i)e, Fibularia trigoiia Lamarck, loc. cit. = Echinocyamus craniolaris Leske, 1778. Add. ad Klein, p. 1.50. 



The species of this genus are known almost wholly from the bare tests. 

 Excepting the Australian species nutriens, I have seen no specimens clothed in 

 spines. The Siboga collected three species in the Dutch East Indies, but appar- 

 ently of only one were there specimens with spines and pedicellariae. Our knowl- 

 edge of these external structures is therefore quite deficient but enough is known 

 to satisfy us that in neither spines nor pedicellariae does the genus differ essen- 

 tially from Echinocyamus. The Albatross has not collected any examples of 

 Fibularia, the specimens from the Hawaiian Islands referred to F. australis in the 

 preliminary report (Bull. M. C. Z., 50, p. 247) proving to be Echinocyamus. 

 More than twenty-five species of Fibularia have been named but the great 

 majority of them were based on specimens of Echinocyamus, on young 

 clypeastroids of other genera, or on individual variants of F. craniolaris. All 

 told there seem to be six valid species in the genus, so far as present knowledge 



