258 Prof. J. Young and Mr. J. Young — On Polypora. 



YI. — Note on the Occukrence of Polypora. tuberculata, Prout, 



IN Scotland. 



By Prof. J. Young, M.D., and Mr. J. Toukg, Hunterian Museum, Glasgow. 

 S the Transactions of the Academy of Science of St. Louis, in 

 which Prout described this species, are not generally accessible, 

 we quote the description at length. 



Bryozoum a fan-like expansion, probably one or two inches wide. 



Longitudinal rays moderately large, pretty uniform in size, suddenly 

 enlarged before and after bifurcation ; dichotomizing at one, one and 

 a half, near two lines apart ; dichotomizing oppositely on two 

 branches from the main branch ; stems scarcely diminished one-half 

 by branching, and rapidly attaining their original size. 



Dissepiments small, about one-third as large as the rays, about one- 

 third the transverse diameter and one-fifth the longitudinal diameter 

 of the fenestrules, slightly depressed, not expanding much at junction 

 with the rays. 



Fenestrules oblong subquadrangular, sometimes shortly spatulate or 

 irregular near the bifurcations, twice as long as broad, slightly 

 broader than the rays, generally opposite. In a space of two lines 

 longitudinally there are three and four-fifths, and transversely five 

 fenestrules ; or in five millimetres there are four longitudinally and 

 six transversely. 



Cell pores small, round, with thin lips slightly raised above the 

 surface, alternate, their own diameter apart, in from three to six more 

 or less regular lines upon each ray, having a very slightly raised keel 

 between them, and having generally on the middle keel an irregular 

 line of round tubercles, which sometimes intermits, and sometimes 

 shows a disposition to become double. Cell pores five, tubercles 

 three or four to each fenestrule. 



Beverse covered by a dense cortical substance, with a few scattered 

 granules. 



A species answering to the above description is the most frequent 

 representative of the genus Polypora in the Carboniferous rocks of 

 the West of Scotland. To what Prout states one or two additions 

 require to be made. The thin lip of the pores in well-preserved 

 specimens is not circular, but sinks down on the lower edge of the 

 aperture, which thus has a pyriform crater shape. In addition to 

 the ridges mentioned by Prout, the intervening surface is covered 

 with very fine short wrinkles, which are sinuous and sometimes in- 

 terrupted, so as to give a tubercular aspect. The fronds sometimes 

 attain a size of three inches. 

 Note on the Mode of Preservation of the Lanarkshire Polyzoa. 



In some localities, but chiefly at Hairmires, near East Kilbride, 

 the stems and fronds of several species are covered with a very thin 

 layer of mineral matter, which veils, but does not conceal the sculp- 

 ture of the surface. The layer likewise extends over the apertures, 

 and may be traced from a narrow diaphragm till it forms a complete 

 operculum. It is most frequently found with a minute central pore; 

 Weak acid removes the polyzoon, leaving the incrusting layer intact; 



