INTRODUCTION. 
xliii 
should be placed in the same species because they both possess 
the same generic characters. 
The recent careful zonal collecting in the English Chalk has 
shown that the Bryozoa are often remarkably restricted in their 
range and may be especially useful as zonal fossils. Thus Br. Rowe 
has shown that Bicavea rotaformis is confined to a narrow band 
just above the base of the Holaster planus zone. The two recent 
Geological Survey Memoirs on the country around Andover and 
around Henley both show that the Bryozoa are practically confined 
to a few horizons, on which, however, they appear to be common. 
Thus near .\ndover ^ there are no Bryozoa recorded in the lists from 
the Lower Chalk (p. 17) or from the Holaster planus zone (pp. 28, 29). 
There is a list of ten species from the J/! coranguinum zone (p. 37), 
identified by Mr. Treacher, but only one of them ranges upward to 
the zones of Harsupites and of Actinocamax quadratus. The 
brachiopods, on the contrary, are more widely distributed and have 
a longer range. 
Again, in the country around Henley,- the memoir includes no 
Bryozoa in its lists from the Lower Chalk (pp. 27, 28) and only 
four species from the Middle Chalk, but it includes a list of thirty- 
eight species and varieties determined by Mr, Treacher from the 
Upper Chalk ; most of these species come from the zone of Micraster 
cortestudinarium . 
In this list of thirty-eight species, seven are confined to the 
Holaster planus zone, five to the zone of Micraster cortestudinarium^ 
and sixteen to the zone of Micraster coranguinum. Of the remaining 
ten species, seven are found both in the cortestudinarium and 
coranguinum zones, two pass from the Middle Chalk up to the 
coranguinum zone, and one passes from the Middle Chalk only to 
the cortestudinarium zone. 
The belief that the Bryozoa are of little zonal value is due to 
old and unreliable determinations. Thus Vine prepared a synopsis ^ 
’ A. J. Jukes-Browne. Partly from Xotes by F. J. Bennett and H. J. Osborne 
White. “The Geology of the Country around Andover.” Mem. Geol. Surv. 
England and Wales. Explanation of Sheet 283. 1908. pp. v -h 67, 12 figs. 
2 A. J. Jukes-Browne & H. J. Osborne White. “The Geology of the 
Country around Henley-on-Thames and Wallingford”: Mem. Geol. Surv. 
England and Wales. Explanation of Sheet 254. 1908. pp. viii -f 113, 13 figs. 
3 G. R. Vine. Rep. Cret. Polyz. : Rep. Brit. Assoc. 1890, p. 386. 
