A NEW GENUS OF STARFISHES — CLARK 499 



separated from each other, all standing on a uniform filmy calcare- 

 ous body investmeni. In the center of the abactinal surface the imbri- 

 cation of the plates is more or less outward, but this soon changes 

 so that the plates on the upper surface of the arms imbricate toward 

 the center of the animal, those on the sides of the arms becoming 

 somewhat oblique and those adjoining the marginals imbricating at 

 right angles to them, toward the midline of the arms. In each in- 

 terradius, about midway between the center of the disk and the 

 interradial angle, there is a single large circular plate with a central 

 elevated boss, which, except for the boss, is entirely concealed by 

 the overlapping of the surrounding plates. 



The elevated portion of each plate bears 1 to 10, usually 4 to 6, 

 short spinelets situated irregularly about its summit, leaving a more 

 or less conspicuous central area bare. These spinelets may or may 

 not be in contact basally. They are cylindrical with roughened or 

 denticulate tips and are short and rather stout, three or four times 

 as long as thick. The groups of spinelets are well separated from 

 one another. In the actinal interradial areas the groups of spinelets 

 tend to become elongated and to be arranged in irregular rows. 



There is no madreporic body, and superomarginals are absent. 



A series of 13 inferomarginals runs from the interradial angle to 

 the arm tip. These are triangular, with the apex of the triangle 

 toward the arm base and the outer portion, which broadly overlaps 

 the base of the inferomarginal succeeding, much swollen. Only the 

 swollen outer portion is visible, so that the inferomarginals appear 

 as much swollen, broadly rounded plates about twice as high as long. 

 They are somewhat larger than the plates just above them and are 

 distinguished particularly by their radial, instead of transverse, 

 imbrication. They bear 5 to 8 spinelets in a double row. 



Between the inferomarginals and the adambulacral plates, and 

 connecting the two series, is a series of very small actinal interme- 

 diate plates that runs to the arm tip. The basal four or five of these 

 plates carry a single spine; the others are without spines. As far 

 as the eighth adambulacral plate a row of very minute plates alter- 

 nates with these at their inner ends. Opposite the proximal six 

 adambulacral plates the actinal intermediate plates become larger, 

 and in the interradial angles between these and the inferomarginals 

 there are about half a dozen small irregularly arranged additional 

 plates. 



There are 18 fully developed adambulacral plates along each side 

 of the ambulacral groove. These are about three times as broad as 

 long, project well above the general surface, and are separated from 

 one another by their own width or more. 



