1881. J NATURAL SCIENCES OF PHILADELPHIA. 263 



inner ray are narrower, truncate below, resting upon the longer 

 upper face of the secondary radials, and support like the outer 

 plates one or two plates in succession, which in turn support the 

 arms. The radials of the higher orders are almost of equal size, 

 and at least twice as wide as high. There is no interradial within 

 the calyx, and no other anal plate but the one described.^ 



Dome highly elevated, pyramidal, pentagonal in outline. The 

 angles which are radial, are excavated for the attachment of the 

 large radial processes. The sides of the pentagon are the inter- 

 radial spaces, which seem to have faint grooves, running longi- 

 tudinally, wherein the arms rest. Four of the interradial spaces 

 are of equal size, the fifth somewhat larger. All five are similarl}^ 

 constructed, and contain three plates in the lower series. The 

 middle or first interradial plate is the larger, its two upper sides 

 forming an angle. The two adjacent plates, as will be explained 

 presently, are representations of radials of a second order. 

 Above these and alternating with them, rests a second series of 

 interradials, composed of two plates, larger than the first, and 

 these meet laterally with corresponding plates of adjacent rays. 

 The upper series, representing the proximal vault pieces, consists 

 of a single plate in four of the spaces, and two slightly smaller 

 ones in that of the posterior side, which all join laterally and 

 form a continuous ring. In a few instances only, there appears 

 to be a small anal plate located between the two smaller proximal 

 plates. 



The first radial dome plates are enormously developed in the 

 form of wing-like processes which form the most characteristic 

 feature of the genus. Succeeding these outward, toward the rim, 

 are two small secondary radial dome-plates, one on each side of 

 the lower interradial, and two still smaller plates bifurcating from 

 the last, which are tertiary radial dome plates, but which are rarely 

 observed. Besides these there is a rather large, very peculiar 

 interbrachial plate, beneath the winged first radial. The winged 

 extensions of the first radial dome plate are very variable in form. 

 They are, according to Wetherby, either spatulate, claviform, or 

 cuneiform ; in some species thin and knife-like throughout their 



* In one of Wetherby" s specimens which he kindly loaned us, we found 

 a little triangular piece resting upon the anal plate. Whether this is ab- 

 normal, or a deviation from the general rule and of specific importance, 

 we are as yet unable to say. 



