478 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



prominent, except in small specimens, and in large specimens not 

 very distinct one from another, the borders being obscured by the 

 dense covering of small, papilliform, blunt or sharp, spinelets (1 

 mm. long in the type). These spinelets are usually more or less 

 swollen on account of their membranous covering and are inclined 

 slightly toward the center of disk, the 2, 3, or 4 central spinelets of 

 each plate being, as a rule, enlarged slightly, especially in large 

 specimens. One of the central spinelets may surpass the others a 

 trifle and be more tuberculate in form, but usually the excess is not 

 at all conspicuous. One or 2 small lanceolate forficiform pedicel- 

 lariae about as long as the spinelets, but more robust, stand on the 

 edge of the papular areas, which in the type usually contain 2 or 3 

 papulae, but in moderate or small-sized examples has generally 1 

 papula. In medium-sized specimens the spinelets are decidedly 

 granular in appearance, owing to the fact that they are relatively 

 shorter and nearly always blunt or truncate. 



Degree of carination of ray variable, best marked in medium-sized 

 specimens (R, 125 mm.) and in large specimens such as the type 

 it is rather more pronounced on the proximal part of the ray. 

 Arrangement of plates and spinelets closely similar to that of Z. 

 carinatus^ but in specimens with R more than 90 mm. there are 

 6 longitudinal series of plates between the adradial and adambu- 

 lacral plates, instead of 5 as described for carinatus. In the present 

 species some specimens of the size of the typa of carinatus (R=90 

 mm.) have 5 series and some 6. Plates of carinal series slightly 

 wider than long, or the 2 dimensions subequal, with 1 or 2 lobes 

 on either side, which overlap the sunken adradial plates, the 

 exposed surface of the latter being one-third or one-half the width 

 of the carinal plates. The next 2 series probably represent the 

 marginal plates. They are wider than long, hexagonal, and the 

 upper series overlaps the adradial plates and the inferomarginals. 

 The exposed surface of the plates of the remaining 4 rows de- 

 creases in width as the furrow is approached, and each bears a sharp, 

 appressed, dagger-shaped spine, which increases in size toward the 

 furrow, where they are about twice the length of their plate. These 

 spines thus form vertical series of 4 along the side of the ray. 

 Toward the end of the ray, after the lowermost series of plates ends, 

 the spines appear on the inferomarginal plates, and sometimes occur 

 here and there, but not numerously, on the proximal inferomarginals. 

 The superomarginals are without central spines. 



All the plates are closely covered with pointed, appressed, papilli- 

 form spinelets, which are directed toward the midradial line, 3 or 

 4 in the center of the carinal plates being enlarged, and forming an 

 inconspicuous tuft. The central spinelet may be enlarged into a 

 short, robust, bluntly pointed tubercle. In some specimens the 



