436 BULLETIN 100, UNITED STATES NATIONAL MUSEUM. 



The student will find the figures a more reliable means of identi- 

 fication than the descriptions, which are susceptible of being mis- 

 understood, or of being stretched to cover variations which they are 

 not meant to include. 



HENRICIA DENSISPINA (Sladen). 



Plate 118, figs. 2, 3 ; plate 119, figs. 1-3. 

 CribreUa densispina Sladen, 1879, p. 432, pi. 8, figs. 5-9. 



Diagnosis. — Rays 5, slender, either subcylindrical or depressed, tap- 

 ering, rather long, but varying according to size; abactinal papular 

 areas about same size, or larger than plates, sometimes including a 

 secondary plate or two within the mesh; papulae usually 1 to 3; 

 spinelets numerous, very delicate, ending in a sharp point or points ; 

 3 regular series of plates adjacent to adambulacral plates, the median 

 the larger; adambulacral plates with 2 or 3 compressed spinelets in 

 vertical series in furrow and upward of 25 on surface. R=:53 

 mm., r=7 mm., R=7.5 r; breadth of ray at base, 7 mm. 



BescTvption. — The meshes of the abactinal skeleton are smaller 

 than in H. arcystata, with usually 1 to 3 papulae. Most of the 

 meshes have no secondary plates and Avhere these are present there 

 are only 1 or 2. Although the trabeculae are narrow, as in arcystafa, 

 the spinelets are more numerous and fully twice as long, ending in 

 several exceedingly delicate points. The abactinal surface has much 

 the appearance of that of the less extreme specimens of HenHoia 

 leinicscula multispina Fisher, while arcystata would correspond to 

 H. I. annectens, but with slenderer, generally smaller spinelets. 



Parallel to the adambulacral series are 3 regular rows of plates, 

 the inner extending two-thirds to three-fourths the length of the 

 ray, the other 2, the marginals, reaching to the tip. The actinal in- 

 termediate and superomarginal plates are subequal, oblong to sub- 

 circular, with 30-35 spinelets. The inferomarginals are larger, sub- 

 triangular (the base distad and slightly excavated or concave) and 

 correspond to the superomarginals in position and generallj'^ also to 

 the intermediate plates, so that the three form a transverse series. A 

 series of single papulae ocur intermarginally and inframarginally. 

 Sometimes the inferomarginals have more the T shape of those of 

 arcystata^ but in that case the spinelets are more numerous and 

 longer. 



Adambulacral plates with 2 or 3 small compressed spinelets form- 

 ing a vertical series on the furrow face. Subambulacral spines 10 

 to 25 on proximal third of ray. An angular group of 6 to 8 con- 

 forms to the angular furrow margin of the plate, of which 5 usually 

 stand on the projecting margin while the other spines rapidly dimin- 

 ish in length, the outer half of the plate being occupied by 15 to 20 

 small spinelets, which grade into those of the actinal intermediate 



