Prof. W. King on Plcurodictyum problematicum. 137 



As regards Michelinia (a genus of the family Favosidda), with 

 which Kocmcr has collocated PlcnroiUctijitm, all its species have 

 long tubular corallites, which, aithotigh agreeing with our fossil 

 in being foraminatcd and longitudinally lineated at their margin, 

 are tilled up, cxce])t at toj), with numerous transverse irregular 

 curving plates, giving them quite a vesicular structure*. There 

 is not the least trace of any transverse plates in Pleurodictijum. 



Thus admitting for a moment that our fossil is a coral, it 

 could not be j)laced either in Puritid(e-\ or luivosilid<e, as defined 

 by Edwards and Ilaime; nor could it, strictly speaking, be placed 

 in eitlier of the more comprehensive groups named Zoantharia 

 perforata and Zoantharia tabulata, to which these families re- 

 spectively belong; it could only be considered as an aberrant 

 form of cither one or the other. 



The resemblances just made out are, however, of considerable 

 value ; for they strongly manifest the side which certain affinities 

 of Pk'urodictyam lean to. These affinities in my opinion belong 

 to parts subordinate to others only occurring in animals higher 

 than the Zoanthairs; I am therefore led to consider them as 

 merely of secondary importance. Hence I may be allowed to 



certain parts of this fossil, I have thought it necessary to give a copy of 

 their description : — " Polypier subdiscoide, soit hbie, soit fixe sur un corps 

 serpuhforme ou sur une coqiiille, a pLateau inferieur reconvert d'unc epi- 

 theqne forte et prcsentant quelques phs concentriqnes ; polypie'rites courts, 

 prismatiques, irradiant en un court faisceau et se terminant sur une sur- 

 face legeremeut convexe ; caliccs jiolygonaux, un jjcu incgaux ; trous de la 

 murailie petits et irreguliers, assez pen nombreux ; les murailles un pen 

 larges. De 20 « 28 cloisons formees par cles poutrelles greles qui avancent 

 jusqu'au centre de la chamhre des polypu'rites ; largeur des calices de 3 a 5 

 millimetres. Ces polypiers n'ont ordinairemcnt que 3 ou 4 centimetres de 

 diametre total." — Vide " ^lonograjjhie des Polypiers fossiles des terrains 

 paleozoiques," inserted in the Archives du Museum, tom. v. p. 210, 1851. 

 The passage I have italicized evidently refers to the fine longitudinal 

 costules (spinulose and plain) intervening between the furrows (punctured 

 and plain) previously described in the text (p. 133). But, with all due 

 deference to the opinion of M^I. Edwards and Ilainie, 1 am strongly dis- 

 l)osed to consider the so-called " cloisons " as simply homologous with the 

 granulations, s])inules and echinated costules seen on the septa of many 

 Zoanthairs. 



* I am much indebted to my friend George Tate, Esq., of Alnwick, for 

 placing in my hands his specimens of Michelinia to enable me to make 

 myself acquainted with the character of this interesting genus. 



t MM. Edwards and Ilaime place Pleurodictyum next to Protarcea in 

 Poritidce. In their " Monographic des Poritides," published in the Annales 

 des Sciences Naturelles, 3 ser. t. xvi. p. 48, referring to their earlier Mono- 

 graph in the 'Archives,' they state— "et nous nous bornerons a repe'ter 

 ici qu'elle differe seulement des Litkarcea par une epitheque plus deve- 

 lopjjce, des murailles plus epaisses et des cloisons plus poutrellaires." 

 Lijhnrcea, another genus of the family Poritides, is typified w ith the Astrea 

 VVebsteri of Bowerbank, — an eocene fossil described and rejnesented in 

 their Monograph of the British Fossil Corals, p. 38. pi. /. fig. 1. 



