TOMES : MESOZOIC CORALS OF THE COUNTY OF YORK. 79 
are divided by much developed and prominent ridges, formed by 
the union of costal prolongations from the septa, and the latter 
are connected by septal costie. 
The sides of the septa have vertical ridges, ending in denti- 
culations on the septal edge. Increase takes place by gemmation. 
The genus is one of the Asfrceidce, and of the Astrceince, and 
has some affinity with with Dimorphastrcea, but differs from it 
materially by having the calices arranged in radiating lines, 
separated by strongly-marked cristiform ridges around the parent 
calice instead of in circles. 
DiMORPHOSMILIA EBORACEXSIS Sp. nOV. PL XX., figS. 1, 2, 3, 4. 
The corallum is subcircular or ovoid, and the outer margin 
is somewhat lobular. The calicular surface varies considerably 
in its degree of convexity, and the outer margin is thick or thin 
according to the elevation of the corallum. 
The basal wall is sometimes nearly flat, but more frequently 
has a central circular depression with a point indicating former 
attachment. It is clothed with a thick epitheca, which is con- 
centrically wrinkled, between the rings of which there are some- 
times costJB, which are straight and uniform in size. 
The valleys are wide and open, but the ridges between them 
are prominent, sub-acute, and the cost?e of which they are com- 
posed meet, blend, and form what has the appearance of a wall, 
but in which no true wall has been determined. There are 
usually five or six of these ridges in a small specimen, increasing 
in number up to eight or nine in a large one. 
The calices are few in number, but there is often more than 
one row in a valley, more especially in specimens of intermediate 
size. When of greater dimensions the rows of calices are nearly 
always single. They are open and superficial, but the fossula 
small and well defined. 
There are four cycles of septa, and a few short ones of 
a fifth. The primary septa nearly meet in the centre of the 
visceral cavity, w^here they are sometimes a little curved. The 
secondary ones are a little shorter than the primaries, and those 
