30 VERRILL 



The row of actinal plates that unites with the adambulacrals, when 

 there are several rows, may be called synactinal, to indicate its func- 

 tion. It may consist either of the peractinals or of subactinals. 



When these rows are very much alike in size and form, mistakes 

 have often been made in descriptions, the peractinal row having 

 often been described as the inferomarginal row or vice versa, or else 

 no distinction has been made by the earlier writers. 



The most positive criterion, in doubtful cases, is to trace these 

 rows of plates to their origin. True marginal rows originate at the 

 ocular plate ; peractinals, when present, often terminate near the 

 ocular ; but other rows generally fail to reach the end of the ray. 



The inferomarginal plates may be directly joined to the adambu- 

 lacrals by a lobe or apophysis, but more commonly there is at least 

 one row of actinal plates between, and sometimes, besides this first 

 or peractinal row (pa), there may be one or more shorter rows of 

 subactinal plates {sa) interpolated proximally. All these plates 

 usually bear spines, but in some cases all the interactinal plates are 

 rudimentary and spineless. 



The secondary dorsal skeleton varies much, but is most commonly 

 chiefly made up of unequal and more or less imbricated ossicles or 

 lobulated plates, with the ends or lobes of adjacent plates over- 

 lapping, so as to leave rather wide papular spaces between them. 

 Or the plates may be broader, somewhat rhombic, lobed, and more 

 closely imbricated, as in Stichaster. In most cases, however, they 

 are also united transversely by smaller connective ossicles. 



II. PEDICELLARI^ OF THE ASTERIID^. 

 Text-figure 2. 



Pedicellarise of both kinds are probably always present in the 

 normal adults, though on some individuals they may be few or 

 lacking. 



The major or forficulate pedicellarias are generally ovate or lanceo- 

 late, sometimes wedge-shaped, stone-hammer-shaped, lyrate, or 

 spatulate. The tips may be acute, plain, flat, or denticulate. 



They are mostly dermal, but may also occur on the ventral and oral 

 spines, or along the inner edges of the grooves, or attached to pedi- 

 cels in clusters within the grooves, or even on the pedicels of the 

 ambulacral feet. They may be of several sizes and forms on one, 

 specimen. 



Certain species of Siichaster, Coronastcr, etc., have a peculiar very 

 large form of dermal pedicellariae, often as thick as the spines, in 



