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| Keywords: The Quarterly journal of the Geological Society of London (12893379215).jpg 118 <br> DK J W GKEGORY ON THE <br> Feb 1897 <br> agree in having perforate non-crenulate tubercles and low broad <br> interambulacral plates each with a row of tubercles But the <br> genera differ widely by the structure of the ambulacral plates In <br> Memipedina the compound <br> ambulacral plates are always Fig 6 ” Ambulacral plates of <br> formed of three primaries Pedina After Duncan <br> and the pore-pairs are a simple <br> vertical series But in Pelan- <br> echinus the pore-pairs are <br> triserial We have therefore <br> to look for its ancestor <br> among the triserial Pedinidae <br> and not among the uniserial <br> Diadematidae to which Hemi- <br> pedina belongs <br> Before following this clue <br> however we must remember that Duncan adopted a course which <br> if agreed upon would prevent the derivation of the Echinothuridae <br> from such specialized Diademoida as the Pedinidae Duncan divided <br> the order Diademoida into two suborders ” the Streptosomata <br> including the Echinothuridae and the Stereosomata including the <br> rest of the order He denned the Streptosomata as follows ” <br> ' Test more or less flexible with external and internal branchiae <br> Ambulacral plates alone continued beyond the peristome to the <br> stoma ' But all these characters also occur among the other <br> suborder the Stereosomata In the pedinid Astropyga and the <br> diademid Helxkodiadema see infra p 121 the test is more or less <br> flexible Both external and internal branchiae are as well developed <br> in Diadema as they are in PJwnnosoma 2 In those of the Stereo- <br> somata which have plates on the peristomal membrane these are <br> always ambulacral <br> Hence Duncan's diagnosis is useless and there is no evidence to <br> show that the Echinothuridae diverged from the main diademoid <br> stem at a very early period We may search therefore among the <br> triserial members of that order for a suitable ancestor for the <br> echinothurids Of all the Pedinidae Pedina is most like Pelan- <br> echinus The interambulacral plates have the same tuberculation <br> for in both genera they are multiserial perforate and non- <br> crenulate <br> The ambulacral plates of Pedina show a series of stages between <br> simple diademoid plates and those of Pelanechinus The ambital <br> plates of Pedina usually consist of three primaries of very unequal <br> size In some cases the middle primary increases so much in size that <br> it crowds out the other two constituents and reduces them to demi- <br> plates fig 6 These demi-plates may even lose any connexion <br> with the vertical suture between the ambulacral and interambulacral <br> areas ; they are thus reduced to the position of klasma-plates on <br> the horizontal sutures between the primaries Plates in this <br> 1 Journ Linn Soc Zool vol xxiii 1890 p 25 <br> 2 F J Bell Ann Mag Nat Hist ser 6 vol iv 1889 p 437 36028863 111130 51125 Page 118 Text 53 http //www biodiversitylibrary org/page/36028863 1897 Geological Society of London NameFound Astropyga NameConfirmed Astropyga EOLID 73076 NameBankID 594039 NameFound Diadema NameConfirmed Diadema EOLID 11119068 NameBankID 4722780 NameFound Diadema NameConfirmed Diadema EOLID 11119068 NameBankID 9538568 NameFound Diadematidae NameConfirmed Diadematidae EOLID 1987 NameBankID 2765282 NameFound Echinothuridae NameConfirmed Echinothuridae EOLID 2962903 NameBankID 7186631 NameFound Pedina NameConfirmed Pedina EOLID 13205073 NameBankID 4286190 NameFound Pedinidae NameConfirmed Pedinidae EOLID 1997 NameBankID 594050 NameFound Pelanechinus NameConfirmed Pelanechinus EOLID 13205043 NameBankID 4286522 Biodiversity Heritage Library The Quarterly journal of the Geological Society of London v 53 1897 Geology Periodicals Smithsonian Libraries bhl page 36028863 dc identifier http //biodiversitylibrary org/page/36028863 smithsonian libraries Information field Flickr posted date ISOdate 2014-03-03 Check categories 2015 August 26 CC-BY-2 0 BioDivLibrary https //flickr com/photos/61021753 N02/12893379215 2015-08-26 17 56 44 cc-by-2 0 PD-old-70-1923 The Quarterly journal of the Geological Society of London 1897 Photos uploaded from Flickr by Fæ using a script | ||||
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