138 Prof. W. King on Pleurodictyum problem aticum. 



state, that our fossil possesses strong collateral affinities with 

 the order Zoantharia. 



The question now comes on for discussion, as to what position 

 Pleurodictyum occupied in the Invertebrate division of the animal 

 kingdom ? As intimated in the early part of this paper, I dissent 

 entirely from the opinion which regards it as a member of the 

 class Corallaria. My own opinion is entirely based on the 

 presence of the vermiform appendage, which I consider a true 

 organic constituent of the fossil; it therefore behoves me to 

 establish its claims to be considered in this light. 



According toLyell and Milne-Edwards, Pleurodictyum attached 

 itself to the vermiform appendage, i. e. the " Serpula " of the 

 former, and the " serpuliform body " of the latter ; but this opi- 

 nion is totally inadmissible from the appendage beinff always in- 

 ternal. Recurring to Phillips^s view, that it is '' a vermicular 

 cast in the tubule of some mollusk (?) which had perforated the 

 coral," it may be observed, in the first place, that as I have not 

 seen specimens from every known locality*, it would be improper 

 of me to assert that Pleurodictyum never occurs without the 

 appendage ; but this I am prepared to state, that, with a few 

 exceptions, every specimen I have examined from Daun possesses 

 it : — in making this assertion I speak advisedly, because possibly 

 some parties may dispute it. I perceive the appendage in the 

 smallest as well as the largest specimens ; and in some of the 

 exceptional cases noted, I can see the vacant space which it ori- 

 ginally occupied. I am therefore led to conclude, that whenever 

 the appendage is absent it has either fallen out, or been removed 

 by some accident. 



The vermiform appendage in all the specimens that have 

 passed under my notice is always folded, as before described, 

 somewhat like the letter S, having its central portion resting on 

 the basal plate, and its extremities passing up to opposite sides, - 

 between the margin and centre, of the upper surface. This con- 

 stancy of form and position it is impossible to conceive could 

 have prevailed had the appendage been a perforating bodyf. 

 Again, this structure is never seen otherwise than passing 



* It is of extensive geographical range, occurring at West Ogwell and 

 Torquay in Devonshire, Nehou in France, Coblentz and other places on 

 the Rhine, Daun in the Eifel, Aleje in Spain, Goslar in the Hartz, and 

 Jefferson County in the State of Indiana, North America. In all these 

 localities, Pleurodictyum occurs in the Devonian system ; but, according to 

 Sir R. Murchison, M . Richter has lately described a new species under the 

 name P. Lonsdalei from the Silurian beds of Saalfeld (vide Quart. Journ. 

 of the Geol. Soc. vol. ix. p. 413). Perhaps Milne-Edwards's Spongarium 

 may be the basal plate of a fossil having some relation to Pleurodictyum ? 



t The two specimens represented under figures 1 & 4. PI. X. are almost 

 a fac-simile of each other as regards both form and position. 



