19 
Septa crenulated, about forty in number, clearly defined almost to the 
centre, apparently uniting there, though in many the central part is occupied 
by secondary deposits. Vesiculose plates continuing through a large 
proportion of the interior of the corallite. No true horizontal diaphragms. 
No wall nor other demarcation between the central and outer areas. 
D. primum can readily be distinguished from D/i halysitoides by its 
more normal form of growth and by its larger and more circular corallites. 
Of the Silurian DipkyphyUums it resembles D. huronicum in the lack of 
true diaphragms and the large proportion of the vesiculose interstices, 
but the considerably smaller corallite differentiates it at once. 
Horizon and Locality . Richmond: Beaverfoot. Between mount Sir 
Douglas and mount Munroe, Palliser pass, at 268 feet above the base of 
the Beaverfoot in the section near the head of Windermere creek in the 
Stanford range, British Columbia. 
Plasmadictyon nov. gen. 
The two specimens described under this genus are not well preserved, 
but they clearly do not belong to any previously defined genus. The 
corallum grows as a low, flat expansion, possibly encrusting some other 
shell. Surface a network of small, irregular corallites, polygonal, circular, 
angular, or crescent shaped, never larger than | mm., many mere tubules. 
Pores, when present, very large. In general form of growth suggesting 
Protarea , but the corallites are not in any degree similar. A more complete 
generic description of this coral will have to await the finding of better 
material. 
Plasmadictyon irregular e n. sp. 
Plate I, figures 11, 12 
Corallum forming thin expansions, the larger of the two incomplete 
specimens found measuring 1£ inches across the piece and the height of 
the growth ranging from 3 mm. to 5 mm. The surface is covered with 
small deposits due to the form of silicification. At times the top of the 
corallite is roofed over. In some cases the deposits are in the form of 
tiny, irregularly rounded nodes, or as minute separate granules; or a 
number run together along the top of the wall of a corallite. No epitheca 
evident, many of the corallites having open ends at the base. The epitheca, 
if present, must have been dissolved away, or if the coral were encrusting 
another form it must have broken from it. In one rather crushed portion 
of the larger corallum there is the crumpled suggestion of an epitheca. 
Corallites upright, very irregular in size and shape, largest tubes generally 
circular, from 5 mm. to f mm. in diameter. Many of these larger circular 
tubes are surrounded by minute tubules which apparently begin in the 
wall and are not yet sufficiently developed to have calices of their own. 
Between these two forms there is every possible variation of size and shape, 
some crescent-shaped surrounding one-half of a circular tube, some angular, 
some more or less irregularly elliptical, in some cases placed as though 
radiating from a central larger one. Some parts show an arrangement 
