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. The 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 oi pleurodictyiim problematkum. 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 parasiiit organism and 

 hence not a proper character of the genus. 



In 1842, De Koninck established the genus Michclima. 

 In 1851, Edwards and Haime in Polyp. Pal. associated under 

 Pleurodictyiim problematicum 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 



