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 pedicellaricC in reality belong to the same natural group. 



It is a serious drawback that the pedicellarise cannot be iised in the classification of the fossil 

 Echinoids. Groom (175), to be sure, has described the pedicellarise of Pclanechinus 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 — generalh' we 

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

 characters, but the\' are far from being alwa}'s 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 loedicellaria; are found in an Echiinis, 

 viz. globiferous 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 ver\' characteristic differences in the different 

 genera. Especiall)' the latter form shows man}- peculiarities. The structure of the blade is highly 

 different; it may be open or shut, the margins ha\iug coalesced on the inside; there ma\" be manv 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'). 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 ujjper 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 pedicellarite in Echijins. Here thus is 

 only one unpaired lateral tooth. In Sphcrrcchiinis^ Strongylocciitrotiis etc. no lateral teeth are found at 

 all, only a little obliquit)^ 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 (Strongylocentrotus} 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 ver\- 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 foin- different kinds of pedicellarise are found in the old families Echinidcr and 

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

 (HapalosoniaJ; they are highly peculiar (PI. XIII, Fig.s. 20, 24, 25), obviously very ])rimitive. The 

 calcareous skeleton con.si.sts of three simple rods lying between the three (mucous?) glands, each 



■) Conip. however, tlic description of the globiferous pedicellarise in Stoitiopitcustes. 



