SHALLOW-WATER STARFISHES 3I 



wliich the broad valves terminate in a series of curved denticles, so 

 that when closed the valves resemble a pair of clasped hands, or 

 better still, a pair of clasped feet of a cat, with the claws protruded. 

 These may be called felipcdal or unguiculate. In many other cases 

 similar gigantic pedicellariae have spatulate valves, with a smooth 

 or denticulate edge. In Pisaster they are sessile, stout, erect, stone- 

 hammer-shaped or wedge-shaped, with serrate or unguiculate edges. 

 (See pi. XLix, figs. 3-3^.) 



These peculiar giant forms are usually accompanied by others of 

 the ordinary ovate form, much smaller in size, and they are usually 

 characteristic of special generic groups. But as such groups are 

 sometimes widely separated, both morphologically and geographi- 

 cally, it is not unlikely that these are survivals of a type of pedicel- 

 larias that, at some remote period, was common to the whole family. 



The minor or forcipulate pedicellariae (text-fig. 2) generally form 

 wreaths or large or small clusters on the spines, but they may 

 also occur, either singly or in clusters, on the integument of the 

 dorsal or lateral plates, on the papular areas, and in other situations. 



III. RELATIVE IMPORTANCE OF MORPHOLOGICAL CHARACTERS 



IN ASTERIID^. 



Perrier, Sladen, Bell, and others who have divided this family, 

 have differed considerably in their estimation of the relative impor- 

 tance of the various morphological characters. 



A. MODES OF GROWTH AND INCREASE IN NUMBER OF SKELETAL PLATES. 



Text-figure i, i-iv. 



The number of ossicles and plates of nearly all kinds, except the 

 primary radials and orals, and the oculars, increase continually dur- 

 ing the entire growth of most starfishes. The size and age have no 

 definite limit, so that unusually large specimens of any species may 

 often occur with correspondingly increased numbers of plates and 

 spines. Therefore the exact number of plates, say of marginals, is 

 of no great importance, e.xcept when specimens of identical sizes or 

 ages are compared. In the early stages of growth, the first dorsal 

 plates that appear are the central, primary interradials, the radials, 

 and the ocular plates. A little later the median dorsal radials and the 

 marginals appear; and the commencement of a row bet^vecn the 

 upper marginals and median row often appears at the same time or a 

 little later. The number of the plates in all the primary rows is 



