Prof. W. King on Pleurodictyum problematicum. 137 



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

 which Roemer has collocated Pleurodictyum, all its species have 

 long tubular corallites, which^ although agreeing with our fossil 

 in being forarainated and longitudinally lineated at their margin, 

 are filled up, except at top, with numerous transverse irregular 

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

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



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

 could not be placed either in Poritid(S-\ or Favositidce, as defined 

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

 in either 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 either one or the other. 



The resemblances just made out are, however, of considerable 

 value ; for they strongly manifest the side which certain affinities 

 of Pleurodictyum 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 subdisco'ide, soit hbre, soit fixe sur un corps 

 serpuliforme ou sur une coquille, a plateau inferieur reconvert d'une epi- 

 theque forte et pre'sentant quelques phs concentriques ; polypierites courts, 

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

 face legerement convexe ; caUces polygonaux, un peu inegaux ; trous de la 

 muraille petits et irreguliers, assez peu nombreux ; les murailles un peu 

 larges. De 20 a 28 cloisons formees par des poutrelles greles qui avancent 

 jusqu'au centre de la chambre des polypierites j largeur des calices de 3 a 5 

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

 diametre total." — Vide " Monographic 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 MM. Edwards and Haime, I am strongly dis- 

 posed to consider the so-called " cloisons " as simply homologous with the 

 granulations, spinules 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 Haime place Pleurodictyum next to Protarcea in 

 Poritidee. 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 repeter 

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

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

 Lithnrcea, another genus of the family Poritidee, is typified with the Astrea 

 Websteri of Bowerbank, — an eocene fossil described and represented in 

 their Monograph of the British Fossil Corals, p. 38. pi. 7- fig. 1. 



