﻿20.2 



DISCOIDEA 



Lister 1 in his ' Hist. Animal. Anglise ' states, in reference to his fig. 20, tab. vii, which is 

 copied from Plott, " Echinites parvulus striis capillaceis undiq ; insignitus," ex D. Plott, 

 fig. 9, tab. viii, " Juxta Teynton agri Oxoniensis inventus est." 



Lang,2 in his ' Historia Lapidum Figuratorum,' says, in reference to " Echinites, striis 

 capillaceis a centro ad circumferentiam undique insignitus, subluteus mediocris rotundus, 

 vertice compresso, basi ex pluribus annulis striatis sibi invicem impositis conflata." I 

 regard the original of Plott's figure not as an Echinite, but as a species of Coral belonging 

 to the family Cyclolitid^e, genus Anabacia ; about Lang's figure I think there can be no 

 doubt, the concentric ridges of the epitheca at the base afford sufficient evidence of the 

 class Anthozoa to which his fossil Coral belonged. Klein's ' Naturalis Dispositio ' is the 

 first work 3 in which we find an undeniable figure of this Urchin ; in tab. xiv, /, m, n, o, he 

 says, " Discoides subuculus ; Kamisol-Knopff : Discuin Germanorum imitans, si versum vel 

 supinum consideramus, a Vertice rosaceo ; quinque seriebus geminis capillaceis et velut 

 acu pictis; in vertice figuram rosulse ferens." Leske, 4 in his 'Additamenta ad Kleinii 

 Echinodermata,' observes, in reference to the figure given by Plott and Lister, " pro 

 Echinite exhibetur ; at vero quantum ex icone coniicere licet, potius Madreporites est, quam 

 Echinites. Nam striae capillacese ex centro progrediunter, ut in Madreporis, neque aliqua 

 oris vel ani mentio fit, prseterea a Plotio Forpites dicitur, quod ipsum nomen Madreporis 

 petrefactis tribui solet. Tanquam dubium corpus, illud itaque omisi." Of Lang's figure 

 Leske says, " mea sententia firma manet, hsec corpora non Echinitas, sed Madreporitas esse." 



The figures of this Urchin given by Parkinson of English specimens, and by Brongniart of 

 French, are very poor; and those of Bronn and Goldfuss of German forms, are not satisfactory. 

 The first real good drawing is that given by Professor Desor in his valuable ' Monograph 

 on the Galerites,' and since then Professor E. Forbes' beautiful plate of this species in the 

 'Memoirs of the Geological Survey,' decade 1, pi. vii, leaves nothing to be desired; 

 subsequently admirable figures have been published in the ' Paleontologie Francaise, 

 Terrain Cretace,' and in the Echinides of the department of the Sarthe, by M. Cotteau. 



The test is small, orbicular, or slightly pentagonal, the upper surface convex, more or 

 less conical, and divided into five broad and five narrow segments by the poriferous zones, 

 which radiate with mathematical accuracy from the circumference of the apical disc, which 

 is small and prominent at the vertex. The under surface is rounded in young and 

 concave in adult specimens, the small, circular mouth-opening lies in a deep central 

 depression, and between it and the posterior margin is a large oblong vent. 



The inter-ambulacral areas at the ambitus are nearly twice the width of the ambulacral ; 

 the dorsal surface of large specimens contains thirteen plates in each column between the 

 apical disc and the basal angle ; the length of the plate varies from the ambitus, where 



1 ' Historia Animalium Anglire,' 1678, tab. vii, fig. 20, p. 220. 



2 'Historia Lapidum Figuratorum Helvetia,' 1/08, tab. 36, figs. 1, 2, p. 126. 



3 'Naturalis Dispositio Echinodermatum,' 1734, tab. xiv, sec. 57, p. 26. 

 * Ibid., Additamenta ad Kleinii, 1778, p. 172. 



