BRYOZOA. 353 



All the dense portions of the zoarium, such as the base, the 

 spiral axis of Archimedes, and diverging supports of Lyropora, 

 a< well as the stony deposit over the front and reverse of the 

 zooecia exhibit essentially the same structure. A finely lami- 

 nated composition prevails throughout, and very delicate ver- 

 tical tubuli, penetrating the laminae, can, as a rule, be demon- 

 strated. The tubuli again are generally arranged in series, and 

 though varying in number are always abundant. 



A- regards zoarial features the genera Semicoscinium Prout, 

 Isotrypa and Unitrypa Hall, and Hemitrypa Phillips, present 

 several peculiarities that have at various times been called into 

 question. The most serious objection to Hemitrypa, which was 

 the only genus of the group generally known, comes from Eng- 

 lish palaeontologists. In a paper entitled "A Review of the 

 British Carboniferous Fenestellidav' published in the Quart. 

 Jour. Geol. Soc. for May. 1879, Mr. G. W. Shrubsole. after 

 quoting some remarks by Lonsdale upon the genus, writes as 

 follows: "There can be no doubt that the interior portion of 

 the Hemitrypa hiheruica (McCoy), is a Fenestella > nor need we 

 be in any doubt as to the species. The difficulty has always 

 been the external sheath. It is important to mention that the 

 same form is parasitic on brachiopods and crinoids, as well as 

 Fenestella. Its connection therefore with Fenestella is accidental 

 and not structural. It is without doubt a small coral common 

 to the limestone, very similar to Flustrx palmata McCoy, the 

 empty calices of which cover over and conceal the Fenestella 

 underneath. Hemitrypa, as we have seen, has Fenestella mem- 

 branacea Phillips for the ground work, and a microscopic 

 coral or polyzoon for the super-structure/' The next year in 

 reviewing the Upper Silurian species of Fenestella. he treates of 

 specimens of F. prisca, Lonsdale, which "are disfigured by the 

 enveloping coral." This species most probably belongs to Uni- 

 trypa. ''The growth of F. prisca is readily detected by the 

 peculiar shape of the so-called fenestrules which are often twice 

 as broad as long. What I take to be the tabulae (!) of the 

 coral occur more frequently than the dissepiments of the Fenes- 

 tella." As regards Mr. S. R. Vine's stand-point it is enough to 

 say he appears to have accepted Mr. Shrubsole's ultimatum 



without examining into the facts for himself. 

 44 



