215 



THE SPINES, PEDICELLARLE, SPH^RIDIA, AND SPICULES. 



Plate 91. 



The spines of the Pedinidse are typically smooth and solid. In the recent 

 species, they form the most obvious distinguishing mark to separate them from 

 the Centrechinidse. The larger primaries are ordinarily very solid, though they 

 may be slender; their length usually exceeds the diameter of the test. They are 

 finely striated, and when pointed (as in C. pulchella), they strongly resemble 

 those of Echinometra. As a rule however, they are not pointed but very blunt 

 and they even may be flaring at the tip. Under the magnifying glass, they reveal 

 the same longitudinal series of minute serrations which is found in many Centre- 

 chinidse, but ordinarily much smaller than in that family. The smaller primaries 

 and larger secondaries are often quite hollow, suggesting how little weight ought 

 to be placed on the characters afforded by the spines. 



The pedicellarise, so far as they are known, show a marked resemblance to 

 those of Centrostephanus. While at least four different kinds occur on most 

 individuals, either globiferous or tridentate may be quite wanting. It seems to 

 be true, as in the case of many other Echini, that if globiferous pedicellarise are 

 abundant, the tridentate are wanting or very rare, while if the latter are abun- 

 dant, the former seem to be missing or infrequent. The stalks of the pedicel- 

 larise are much as in the Centrechinidse, those of the tridentate and ophicephalous 

 rather stout and a little enlarged at the upper end, while those of the globiferous 

 are very slender, scarcely more than a single rod at the middle, and are abruptly 

 enlarged where they join the head. The valves of the globiferous pedicellarise 

 are more or less concealed by the glands, which are often heavily pigmented. 

 They are quite small and terminate in 2-4 teeth. These teeth may be very long 

 (PI. 91, fig. 18) or quite short (fig. 17). The tridentate pedicellarise vary greatly 

 in size and form (PI. 91, figs. 1, 4, 5, 6) but the valves are nearly always narrow 

 and compressed. The heads range from .20 to 4 mm. in length, while the stalks 

 may hardly equal them or may be several times as long. The valves are either 

 straight or curved and may be in contact for most of their length or only just 

 meet at the tip. The ophicephalous pedicellarise are more or less common and 

 occur with valves of two quite distinct forms. That one which is really char- 

 acteristic (PI. 91, figs. 14, ^0) is very greatly constricted at the base of the blade, 

 while the other is broader (fig. 15) or longer (fig. 7) and much less constricted. 

 The latter form intergrades with the tridentate pedicellarise and have been 



