ECHINANTHUS TESTUD1NAKIUS. 515 



anus is frequently its own diameter from the outer edge, but quite as often 

 on the edge itself. The test is depressed ; the outline is somewhat elongated, 

 pentagonal, with rounded angles and slightly re-entering interambulaeral 

 sides. Ambulacral petals comparatively much shorter than those of E. ro- 

 saceus, narrower, more elongated ; interporiferous zone often slightly raised ; 

 apical system small. Actinostome larger in comparison than that of E. ro- 

 saceus. Tuberculation of the test, both above and below, distant, and 

 smaller than in the Atlantic species. The most striking differences between 

 the Atlantic and Pacific species are at once seen on examining the interior. 

 The double walls are limited to the edge of the test ; the lower floor is 

 single, as in Clypeaster, as well as the whole of the abactinal floor from a 

 short distance beyond the extremity of the ambulacral petals ; the pillars 

 connecting the floors, which are so massive in E. rosaceus, are more slender 

 and more numerous, less soldered together ; and the whole of the lower and 

 upper floors is lined with short limestone, needle-like pillars, rising only a 

 short distance from each floor, resembling remarkably the structure of the 

 interior in Clypeaster scutiformis, in which, however, there is no double 

 floor at the edge of the disc. This species is interesting as showing the 

 possibility of a passage between the Clypeastroids, with single and double 

 floors. So that the position of C. scutiformis is by no means certain until 

 we are sure that the specimens described are really full-grown, and that we 

 may not, in the adult of that species, have gradually developed, with in- 

 creasing size, the structural features of the species just described. The teeth 

 are also proportionally much flatter and less powerful than in E. rosaceus. 

 For a figure of a section of this species see Verrill's Notes on Radiata, PI. 



X.f. 7, 7". 



Australia ; Japan ; Sandwich Islands ; Gulf of California. 



