OF DENISON UNIVERSITV^. 
133 
base of the corallum is flat; there being no polyps here to connect 
the casts show no traces of connecting perforations. This base of the 
corallum we know from analogy to have been covered by an epithecal 
membrane, but that part of the cast has not been seen. d"he upper 
surface of the corallum was broadly convex. The separate polyps 
were internally grooved longitudinally. The grooves are shallow, 
and rounded, and vary in number. There are usually from 25 to 30 
of them in each polyp cell, and 10 to 12 of these are usually found on 
that side of the polyp which lies against the epithecal membrane in 
basal polyps. Between these grooves are raised areas or ridges, also 
rounded, bearing numerous low, round, pointed tubercles. They 
are so small that they do not merit the name of spines. These spines 
may occur as a single irregular series, or in two or three irregular 
series. Sometimes they are very irregular in arrangement, at other 
times the arrangement in series is verv readily noticeable. All these 
variations take place in the same corallum. The earlier formed basal 
cells are usually pressed more or less out of shape below on one side, 
so as to form a pseudo -base. 'Those later formed have quite regular 
polygonal outlines, excepting that the side adjacent to the epithecal 
membrane is always larger than the rest. Diameter of base of coral- 
lum 29 mm. A much smaller specimen, 12 mm. broad presents every 
feature of the former excepting that there is a polyp cell in the centre 
flattened around the very base so that the pseudo-base is radiably 
striated, and the longitudinal ridges along the cell walls are more 
prominent, It seems however to be merely a young specimen. 
In 1829, Goldfuss in Petref. Germ, published a fossil under the 
the name of pleiirodictyiim problematiciim. This is entirely similar to 
the Australian species generically, differing however strongly in the 
possession of a tubular coiled body which is more or less interwoven 
with the base of the coralites. This body is found to be frequently 
not present and hence is regarded as only a parasitit organism and 
hence not a proper character of the genus. 
In 1842, De Koninck established the genus Michclinia. 
In 1851, Edwards and Haime in Polyp. Pal. associated under 
Pleurodictyum prohlematicum Goldfuss three distinct types. The first is 
that described by Goldfuss. The second consists of a colony of 
polyps without vertical ridges or series of tubercles. The third has 
vertical ridges but no tubercles. A fourth specimen had vertical 
