308 THE PROCEEDINGS OF THE LINNEAN SOCIETY 



well developed in three cycles and six systems, not corresponding 

 to the costse. In some specimens there are a few septa of a fourth 

 cycle. Alt. 6 to 10, long. 3 to 5, lat. 1| to 2 mil. 



Sphenotrochus excavatus, n. s., PI. 4, Fig. 1, a, b, c. 



Corallum tall, broadly cuneiform, only slightly narrower and 

 more compressed at the base ; calice elliptical, the axis being as 

 4 to 3 ; ends of major axis somewhat depressed below minor ; 

 septa moderately exsert, smooth, except a granular exterior 

 margin, sending forth many long processes into the fossa which 

 sometimes curve upwards and at the base unite with the colu- 

 mella ; in six systems of three cycles, primaries and secondaries 

 nearly equal, tertiaries almost rudimentary, but very thick and 

 becoming stouter outside the wall ; fossa very deep and open ; 

 columella a narrow short lamellar plate projecting very little 

 above the base of the calice, scarcely extending horizontally one- 

 sixth of the length of the major axis ; costse in systems corres- 

 ponding to the septa, the primaries and secondaries suddenly 

 thickening and becoming very coarsely granular and rugged to 

 the base, especially laterally, where they almost assume the form 

 of crests or ridges ; tertiaries continuous and simple, desisting at 

 about one-fourth from the base ; all very granular and almost 

 crested. Port Jackson, rare. J. Brazier. Alt. 10, major axis 6, 

 minor 4 \, at base 5 and 2 \. 



Genus Smilotrochus, M. Edw. 8f H., 1851. 



Corallum simple, straight, cuneiform, free and without trace of 

 adherence ; no columella ; septa finely granular, a little exsert ; 

 wall bare, showing simple distinct costse. Further on I have 

 given reasons why this fossil should be considered the type of a 

 new genus. 



Smilotrochus vacuus, nobis. 



This is a fossil species from the Muddy Creek which has been 

 described by me and figured in the Proceedings of the Roy. Soc, 

 N. S. W., for 1877. All the known species have the septa 

 united or confluent at their inner edge, but this species has a 

 deep well in place of the columella. 



