36 VERRILL 



together such unlike forms as Coronaster of the North Atlantic and 

 Stichaster of the South Pacific forms that evidently belong to dis- 

 tinct families. In the case of Pisaster, our eight species, though so 

 different in their dorsal spines, all have similar and peculiar erect, 

 stout, unguiculate pedicellariae of a type rarely to be found in other 

 groups. 



Some of the remarkable forms of pedicellariae are probably sur- 

 vivals of such structures present in remote ancestors, common to this 

 and the allied families in former geologic periods, rather than 

 structures independently developed in diverse genera, now living in 

 different oceans. Their complexity of structure seems to be too 

 great to have arisen independently in modern times. 



F. MADREPORITE OR MADREPORIC PLATE, AND SURROUNDING SPINES. 



Several writers have made considerable use of the character of 

 this plate. In some of the species having more than six rays, or a 

 variable number, there may be two or more madreporites. Such 

 species are also, in most cases, subject to fission, as in Coscinasterias, 

 Stephanasterias, etc. The number of madreporites is variable in 

 each species of this kind, while closely related species may have but 

 one. The madreporite is sometimes surrounded by a definite circle 

 of special spines (echino placid Bell), 1 but in closely related species 

 no such regular circle of surrounding spines exists. 



In some cases different specimens of the same species may vary 

 in this respect. Therefore it cannot be considered a character of 

 more than specific value, and sometimes not even varietal. Bell, in 

 his arrangement, appears to have given too much importance to it. 

 The same remarks, as to variability, apply to a naked groove or 

 narrow channel that sometimes surrounds the plate. The relative 

 position of the plate and the number and arrangement of its gyri 

 vary in different species, and also greatly with age, but are of some 

 specific value in certain cases, as is also its color, in life. 



G. JAWS AND ORAL SPINES. 



Text-figure 3. 



The jaws in this family consist of an apical jaw-plate, composed 

 of the first and second pairs of adambulacral plates closely united 



1 Among the northwestern American species that are usually " echinoplacid " 

 are L. aqualis, A. katherince, A. acervata, L. epichlora (variable), L. coei, 

 E. troschelii (variable), etc. In general, species with small and numerous 

 spines are apt to have this character. It is particularly conspicuous in Cosmos- 

 terias lurida. 



