SHALLOW- WATER STARFISHES 197 



Subfamily PYCNOPODIIN^. 



Family Pycnopodidce (pars) Stimpson, op. cit., i86i, p. 261. 



Family Pycnopodida Fisher, op. cit., 1906&, p. 136 (with Rathbunaster F.). 



Disk broad and flat, with numerous rays, increasing with age by 

 the interpolation of new rays by budding in successive pairs bilater- 

 ally, at least in the type. 



Dorsal skeleton feebly developed, the ossicles in part united only 

 by thick integument. Spines few, scattered. Pedicellariae usually 

 large and numerous, of two kinds. Adambulacral plates mostly 

 monacanthid. Marginal plates distinct. Interactinal plates small or 

 lacking. Body-cavity without the circular disco-brachial partition, 

 present in Heliasterinae. 



A pair of gonads ; a pair of retractor muscles ; and a stomach-lobe 

 for each ray. Interbrachial septa feebly developed. Podia large, 

 mostly in four rows in adults, often biserial proximally and in young, 

 Ambulacral plates not much crowded, sometimes partially alternate 

 in rays that are bent laterally. 



This subfamily includes, among living species, only the genera 

 Pycnopodia and Rathbunaster, each with a single species, Rathbun- 

 aster californicus Fisher is from off San Diego, California, in 339 

 fathoms. 



Some fossil starfishes from the Devonian closely resemble this 

 group. 



Genus Pycnopodia Stimpson, 



Pycnopodia Stimpson, Proc. Boston Soc, Nat. Hist,, vni, p. 261, 1861. Perrier, 

 Revision, Arch. Zool. Exper., iv, p. 353, 1875. Viguier, op. cit., vii, p, 109, 

 pi. V, figs. II, 12, 1878 (odontophore, etc.). A, Agassiz, North American 

 Starfishes, p. 100, pi. xiii, 1877 (structure of skeleton). Sladen, Voy. 

 Challenger, xxx, pp. xxxix, 560, 830, 1889. Ritter and Crocker, Proc. 

 Wash. Acad. Sci., 11, p. 247, plates xiii, xiv, 1900 (increase of number of 

 rays). Loeb, Publ. Univ. Calif., Physiol., 11, pp. 5-30, 1904 (experiments 

 in hybridization). 



Disk large, covered with a thick, soft integument, in which are 

 few, mostly detached, elliptical ossicles, some of which bear slender 

 isolated spines. Clusters of minor pedicellariae are also scattered 

 over the surface, and in large specimens there are usually many 

 large, scattered major pedicellariae, Rays variable with age, up 

 to twenty to twenty-four in the adult. Their increase is by the inter- 

 polation of new rays, usually symmetrically in pairs, between the 

 older ones, Superomarginal and inferomarginal plates are ventral. 

 They form two regular parallel rows, close together, united by the 



