96 HAWAIIAN AND OTHER PACIFIC ECHINI. 



large primaries almost always cover more or less of the sternum and not infre- 

 quently the posterior oral parts of interambulacra 2 and 4. Primaries do not 

 often occur in the ambulacra and as a rule the oral portions of all the ambulacra 

 are bare, not only of primaries but of secondaries too, and carry only a few 

 widely scattered miliaries. When primary spines occur above the ambitus, they 

 are usually conspicuous and have considerable taxonomic importance. They 

 may attain a considerable length, even up to 90 mm. Such primaries are 

 generally attenuate, often prickly on the distal half and frequently, if not always, 

 are hollow. They are very fragile and it is unusual to find any considerable 

 number of them unbroken in museum specimens. Primaries may be borne 

 singly, only one on each plate, but this is unusual. More commonly several 

 occur on the same plate and sometimes the surface of the plates (on the sternum 

 for example) is completely covered with primary tubercles. It is of interest 

 to note that the large tubercles in spatangoids are nearly always perforate, as 

 in clypeastroids and the primitive regular Echini. In some genera, the primary 

 tubercles become deeply sunken into the test, giving rise to curious swollen 

 rings on its inner surface. Only in Echinoneus are there "glassy tubercles" 

 on the test comparable to those in many clypeastroids. 



The pedicellariae are extraordinarily diversified but they give little help 

 in the attempt to trace relationships within the group. I have not found it 

 practicable to use them to any extent in defining the larger groups, though they 

 are sometimes useful in distinguishing genera and frequently furnish excellent 

 specific characters. Unfortunately the characteristic forms are often very rare 

 or at least hard to find and they are not infrequently wanting in certain indi- 

 viduals. At least five distinct classes of pedicellariae can be distinguished, 

 the globiferous, ophicephalous, tridentate, rostrate, and triphyllous. The 

 globiferous are those which have what appear to be poison-glands associated with 

 each valve; there are always three valves and these usually have a more or 

 less tubular blade and terminate in conspicuous teeth; in some peculiar forms, 

 however, the blade is quite flat though narrow; the glandular tissue may cover 

 the valve or be confined to either its base or its tip; these pedicellariae furnish the 

 best specific characters but unfortunately they are the most frequently missing 

 of the five kinds. Globiferous pedicellariae when present are usually to be 

 found on or beside the bare ventral ambulacra. But they may occur about 

 the peristome or on or near the periproct. 



The ophicephalous pedicellariae are also very frequently wanting, but 

 when present often furnish excellent specific characters. It is a very inter- 



