8 ECHINOIDEA. I. 



be sure, the material has not been sufficient for a thorough examination of all characters with regard 

 to some groups (especially the Cidarids), but I think that from the results found elsewhere we shall 

 be justified in supposing that it will appear everywhere to be a fact that forms with the same kind 

 of pedicellarise in reality belong to the same natural group. 



It is a seriotis drawback that the pedicellarise cannot be used in the classification of the fossil 

 Echinoids. Groom (175), to be sure, has described the pedicellarise of Pelancchinus corallinus in a 

 very well preserved state, and it will, no doubt, also be possible to find them in well-preserved speci- 

 mens of other fossil Echinoids; of course, however, it will always be a rare thing -- generally we 

 have here to be content with the tests (and the spines). These structures also often give excellent 

 characters, but they are far from being always reliable. The former great incertainty in the determi- 

 nation of the recent forms of regular Echinoids (and I think it is not much better with regard to the 

 irregular ones) may be taken to imply that there cannot be any great certainty in the classification 

 of the fossil forms either. 



As is well known, no less than four different kinds of pedicellariae are found in an Echinus, 

 viz. globiferoiis pedicellarise, tridentate, ophicephalous, and triphyllous ones. Of these forms the tri- 

 phyllous and ophicephalous ones have only very little systematic importance; they are very much alike 

 in almost all Echini. The tridentate ones give often excellent specific characters; the globiferous ones 

 are generally very much alike in related species, but show very characteristic differences in the different 

 genera. Especially the latter form shows many peculiarities. The structure of the blade is highly 

 different; it may be open or shut, the margins having coalesced on the inside; there may be many or 

 few teeth along the edge, placed symmetrically or unsymmetrically, or teeth may be quite wanting. 

 On the other hand no forms are known with more than one end-tooth 1 ). When Perrier (op. cit.) 

 says that the globiferous pedicellarise in the Echinometrids end in two hooks, one placed a little above 

 the other, this statement is not quite correct. There is also here only one end-tooth, with the men- 

 tioned open canal on the upper side; the other one that is placed below the former, is a lateral tooth 

 with no poison-canal, homologous with the lateral teeth of the pedicellariae in Echinus. Here thus is 

 only one unpaired lateral tooth. In Spharcchimis, Strongylocenlrotus etc. no lateral teeth are found at 

 all, only a little obliquity is seen towards the end of the blade, a little process on one side, perhaps a 

 reminiscence of the unpaired lateral tooth in the Echinometrids. Some (Strongyloccntrotus) have a 

 long, muscular neck between the stalk and the head; in most forms the head is placed directly on 

 the end of the stalk. Even the structure of the stalk is very different, in some forms it is a per- 

 forated tube, in others some thin calcareous threads, irregularly connected by short cross-beams, or it 

 may even be a single thin calcareous thread. Some forms have large mucous glands on the stalk. 

 In the Cidarids the stalk is very peculiar, with an upper thin part and a lower thick one; at the 

 transition between the two parts a limb of projecting calcareous ridges is often seen. 



The mentioned four different kinds of pedicellarise are found in the old families Ec/iinida- and 

 Echmomeiradce. In the Echinothurids globiferous pedicellarise are only found in a single genus 

 (Hapalosoma); they are highly peculiar (PI. XIII, Figs. 20, 24, 25), obviously very primitive. The 

 calcareous skeleton consists of three simple rods lying between the three (mucous?) glands, each 



T ) Comp. however, the description of the globiferous pedi'cellarioe in Siomopneitstes. 



