624 



MOLLUSCOIDEA. 



appearance (fig. 453). In some cases, as previously noted, the dor- 

 sal or non-poriferous side is traversed by remote, thick-walled, and 

 comparatively large tubes (fig. 467, a), which may project above 

 the surface of the polyzoary, and which may, perhaps, have served 

 for the support of processes similar to the " avicularia " of the recent 

 Polyzoa. In certain forms of the Fenestellidce (species of Fenestella 

 and Polypord), it has been shown by Mr John Young that the poly- 

 zoary was furnished on its margins or external surface with certain 

 remarkable appendages, which were originally described by Professor 

 Martin Duncan and Mr Jenkins under the name of Palaocoryne, 



Fig. 468. — Branched appendage of a Fenestellid (the Paheocoryne radiation of Duncan and 

 Jenkins), enlarged fifteen diameters. (After Martin Duncan and H. M. Jenkins.) 



and which were regarded by these observers as belonging to the 

 Hydrozoa. The appendages in question (fig. 468) are of small 

 size, and have the form of short, robust, calcareous stems, which 

 spring from an expanded base, and are usually marked with longi- 

 tudinal flutings or superficial granulations, while the free extremity 

 generally terminates in a whorl of similarly fluted and ornamented 

 cylindrical processes. In some cases, as shown by Mr John Young, 

 the terminal processes may be curved or hooked, or they may be 

 even united by lateral cross-bars. The observations of Mr Young 

 prove conclusively that the structures described under the name of 

 Palceocoryne truly form parts of the Polyzoan to which they are 



