3 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 faet that forms with the same kind 

 of pedicellariæ in reality belong to the same natural group. 



It is a serious drawback that the pedicellariæ cannot be used in the classification of the fossil 

 Echinoids. Groom (175), to be sure, has described the pedicellariæ of Pela7iechinus coralliuns in a 

 verv 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) ma}- 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 pedicellariæ are found in an Echiiuis, 

 viz. globiferous pedicellariæ, 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 man)- peculiarities. The structure of the blade is highly 

 different; it may be open or shnt, the margins having coalesced on the inside; there ma\' be many or 

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

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

 says that the globiferous pedicellariæ 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 pedicellariæ in Echinus. Here thus is 

 onl}- one unpaired lateral tooth. In Spliærccliiniis^ Strongylocentrohts etc. no lateral teeth are found at 

 all, onl}- a little obliquity is seeu towards the end of the blade, a little process on one side, perhaps a 

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

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

 the end of the stalk. E\'en 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 pedicellariæ are found in the old families Echinidæ and 



Echinometradæ. In the Echinothurids globiferous pedicellariæ are only found in a single genus 



(HapalosoviaJ] they are highly peculiar (PL XIII, Figs. 20, 24, 25), obviously very primitive. The 



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



') Comp. however, the descriptioii of the globiferous pedicellariæ iii Stonwpneiisies. 



