SHALLOW-WATER STARFISHES 



35 



the plates, each plate bearing one or two spines, and then they may- 

 be very reliable guides, in case the specimens are adult. The number 

 of plates or spines in a row, and often, also, the number of rows, 

 increase with age. The supplementary or connective ossicles, when 

 present, also increase with age, and may bear corresponding spines. 

 Mr. Bell, in his arrangement (1881, p. 502), made a special dis- 

 tinction between those species that bear certain spines on isolated or 

 special dermal ossicles (antacanthid) and those that bear spines only 

 on the regular skeletal ossicles (typacanthid). But the special der- 

 mal ossicles, at least in most cases, seem to be merely new skeletal 

 ossicles in process of formation, which are destined, a little later, 

 to become articulated with the older ossicles. Hence this character 

 seems to be of little importance and variable according to the age of 

 the specimens, in most species. 



b 



Fig. 2. 



Minor pedicellarix of Pycnopodia helianthoides (a, b) ; profile views. X 146. 



The dorsal and marginal spines may be similar or dissimilar. The 

 spines may be large and long, or slender, short and thick, or capitate. 

 They may stand singly on the plates, or in groups, or they may be 

 reduced to the form of small spinules covering the plates in large 

 numbers, or even nearly to granules, but they do not form paxillae 

 nor pseudopaxillae. 



E. PEDICELLARI^ ; SPECIAL FORMS. 



Peculiar or unusual forms of major pedicellariae occur on many 

 species, and sometimes species of the most diverse structures and 

 belonging to widely separate faunae will agree in having some of 

 the felipedal type, mentioned above. Such special forms of pedicel- 

 lariae are doubtless of great value for indicating community of origin 

 and generic affinity, when they occur on species that are otherwise 

 structurally similar; but they must not be made to overshadow other 

 structural features, for that would lead to absurd results, as bringing 



