SHALLOW-WATER STARFISHES 39 



same parent may have different numbers of rays. Thus those carried 

 by six-rayed parents of L. epichlora alaskensis, were found to be 

 mostly six-rayed ; but about five per cent were five-rayed, and a few 

 were four-rayed. (See below, and pi. LXXXV, figs. 2, a-/.) 



In other species and genera the number of rays is extremely 

 variable, as in Coscinasterias, where they vary indifferently, from six 

 to eleven or more. In Pycnopodia, additional rays bud in between 

 the older ones in pairs during growth, so that the adult may have 

 twenty to twenty-four rays. This variation is complicated in most 

 species of the former group, and in Stephanasterias albula, by their 

 remarkable habit of spontaneous fission (autotomy) and subsequent 

 irregular replacement of the lost rays by each half. (See pis. LXXIII 

 and LXXIV.) 



J. ARRANGEMENT OF THE AMBULACRAL FEET OR SUCKER-TUBES. 



These are generally arranged in four crowded rows in each 

 groove, or sometimes in two zigzag rows, one on each side of the 

 median line. But in many of the larger species with broad rays, as 

 in the genus Pisaster, they may form six or even eight rows, espe- 

 cially subproximally. Pycnopodia has four rows of sucker-feet sub- 

 proximally, and two rows proximally and distally when adult. 



K. MODES OF DEVELOPMENT ; BROODING OF THE YOUNG J POSITION OF 



THE GENITAL PORES. 



Two widely diverse methods of development occur in the 

 Asteriidae, as described above (p. 7). So far as now known, those 

 genera that carry or brood their eggs and young (padophoric species} 

 also have their genital pores situated on the actinal side, near the 

 mouth ; while those that disperse their minute eggs, and whose young 

 undergo a prolonged, free-swimming larval existence, have the geni- 

 tal pores in the dorsal interradial areas. It is probable that this dif- 

 ference is the most important morphological character by which the 

 family, or at least the Asteriinse, can be divided into large generic 

 groups. Unfortunately this feature has not been noted nor studied 

 except in the case of a small number of the genera and species, so that 

 at present, it can be utilized only in a limited number of genera. 



CLASSIFICATION OF ASTERIID^. 



As defined above, the Asteriidse would include, as subfamilies, 

 Asteriinae, Stichasterinse, Pycnopodiinae, and Heliasterinae:=Helias- 

 teridae Sla. 



