53 



tlie same fossil bed — e.g., the mollusca — are much invested with 

 concretionary calcareous matter. This peculiarity was commented 

 upon by Messrs. Hall and Pritchard when describing the 

 geological section.* 



The costse, which are minutely granular, are continuations of 

 tlie septa, and vary in size according to their position on the 

 corallum, and not according to their cyclical order. On the 

 central portions of the anterior surfaces they are subequal and 

 comparatively slender, and then gradually increase in thickness 

 to the lateral primaries, which for such a small coral are very 

 stout. At the actual margin of the calice the difference in the 

 thickness of the costpe is inconsiderable, but the central ones 

 rapidly diminish in size as they recede from the summit, while 

 those at the ends become, if anything, a little stouter. In the 

 four lateral systems all the costte are free to the base, but in each 

 central system, while the primaries remain free, the tertiaries 

 fuse with the enclosed secondary low down on the wall. The 

 intercostal spaces are narrower than the costse, and are regularly 

 fenestrated by a series of numerous transverse bars and inter- 

 vening cavities, which, in this species, I regard as real pores 

 penetrating the theca. I have decided this latter point on a 

 single example, which was accidentally fractured for a short 

 distance down an intercostal space. Four or five of the cross 

 bars are left intact, and show a clear passage between each from 

 the outside of the corallum to the interior. In other more perfect 

 individuals this delicate characteristic is practically obscured by 

 the calcareous coating previously referred to. 



Average height of coralla, 6-2 mm.; a long one measures 

 8-2 mm. The calices are almost uniform in size. The diameters 

 of the type are 3'2 mm. and 1-9 mm, 



Localify. — Lower beds (Eocene) at Maude. Numerous 

 examples. 



I have great pleasure in naming this species after Mr. J. F. 

 Mulder, my companion in many geological excursions. 



EXPLANATION OF PLATE. 

 Plate II. 



L Section of wall of I'r em at ot rochus fenestratus, dra.wn under the micro- 

 scope with transmitted light. Highly magnified. 



2. Trtmatotrochus Kitsoni. a, corallum, 5 diam.; b, calice, 8 diani ; 



c, section of corallum showing structure of wall, 5 diam. (These 

 three drawings represent diJBFerent specimens.) 



3. Trematotrochus dedivis. a, corallum, 3 diam.; b, calice, 6 diam. 



4- Trematotrochus Midderi. a. corallum, 5 diam.; b, calice of another 

 specimen, 10 diam. 



* The Older Tertiaries of Maude. Proc. Roy. Soc, Vic, 1894, p. 18' 



