198 VERRILL 



broad descending apophyses of the upper plates, with large inter- 

 vening papular areas. The upper plates are large, deeply three-lobed, 

 and usually bear a single large spine. The lower plates are rather 

 smaller, less strongly lobed, and usually bear two large divergent 

 spines. Adambulacral plates are crowded, oblique, bilobed distally, 

 and each bears a single slender spine. Adoral carina is long, contain- 

 ing twelve or more pairs of contingent ossicles. Two large and two 

 smaller peroral spines. Oral area large. 



This genus is peculiar to the west coast of North America. It con- 

 tains only a single species, which is one of the most common and 

 most characteristic littoral and shallow-water starfishes, from Puget 

 Sound to Yakutat, Alaska. It lives among stones at and below 

 low-tide mark. 



PYCNOPODIA HELIANTHOIDES (Brandt) Stimpson. 



Plate XXIX, figure i ; plate xxx ; plate xxxi, figures i, 2 ; plate Lxxin, figure 

 i; plate lxxiv, figures 1-30 (young), figure 6 (pedicellariae) ; plate 

 Lxxxviii, figures ^-^d (details); text-figure No. 2 (pedicellariae). 



Asterias helianthoides Brandt, Prod. Desc. Anim., Mertens, p. 71, 1835. 

 Stimpson, Journ. Bost. Soc. Nat. Hist, vi, p. 89, 1857 (no description). 



Pycnopodia helianthoides Stimpson, Proc. Boston Soc. Nat. Hist., viii, p. 

 261, 1861. Verrill, Trans. Conn. Acad. Sci., i, pp. 324, 326, 327, 1867 (no 

 description). Perrier, Revision, Arch. Zool. Exper., iv, p. 353, 1895 (no 

 description). A. Agassiz, N. Amer. Starfishes, p. 100, pi. xiii, 1877 

 (structure). Whiteaves, Trans. Royal Soc. Canada, iv, p. 116, 1887 (dis- 

 tribution). Ritter and Crocker, Multiplication of Rays and Bilateral 

 Symmetry, Proc. Wash. Acad. Sci., 11, pp. 247-274, pis. xiii, xiv, figs, 1-13, 

 igoo. Clark, Proc. Boston Soc. Nat. Hist., xxix, p. 329 (no description). 



Disk broad and soft. Rays in the adult are usually from eighteen 

 to twenty-four, most frequently an even number, but those with odd 

 numbers are not rare. I have seen them with fifteen, seventeen, 

 nineteen and twenty-one rays. In the young the number varies from 

 six to twelve or more. The increase is brought about by the budding 

 in of successive pairs of new rays, in interradial angles situated 

 symmetrically, as shown by Messrs. Ritter and Crocker.* Sometimes 

 odd new rays appear in other places. (See also our pi. xxxi.) The 

 radii in the rather small dry specimen figured on our pi. xxix, are 

 75 mm. and 182 mm. ; ratio, i : 2.42. 



The rays are rather slender and regularly tapered, covered dorsally 

 by a soft skin, which bears, chiefly toward the ends of the rays, a few 

 scattered, slender spines attached to slender, detached ossicles. On 



^ Proc. Wash. Acad. Sci., ir, p. 247, pi. xiv, 1900. 



