The relative insolubility of the fossils, in comparison with 

 the matrix, has led to their weathering out in strong relief. 

 It is highly probable that the original skeleton of the organism 

 was calcareous, and that the present form is that of a siliceous 

 pseudomorph, in a similar way that many of the Archceocya- 

 thincE, in the Cambrian of South Australia, are preserved in 

 the form of siliceous casts. The interlaminar spaces, now filled 

 with the rock matrix, may possibly represent the chambers 

 that contained the protoplasmic material of the living organ- 

 ism ; or, otherwise, some portions of the skeleton that failed 

 to fossilize. 



The present species differs from the type (G. proliferum, 

 Hall) in the greater independence of the columns, and also 

 in their more regular arrangement. 



Cryptozoon tessellattjm, sp. nov. 

 Plates iii. and iv. w 



Among the specimens sent down by Dr. Chewings are 

 three which possess features somewhat different from those 

 just described. In this form the columns are almost en- 

 tirely calcareous, and vary greatly both as to size and shape. 

 In transverse sections they may be circular, sub-circular, 

 quadrate, angular, or irregular in form, and are frequently 

 confluent and branching. Notwithstanding their great di- 

 versity of shape they maintain a very regular arrangement 

 in relation to each other, the intercolumnar spaces being 

 uniform throughout. This form of growth, together with the 

 fact that the fossils and the limestone matrix weather uni- 

 formly, gives a curious tessellated or mosaic appearance to the 

 specimens. So far as can be determined from the limited 

 material at command the laminae of the columns are similar to 

 those described in the preceding species. 



The distinctive features in the present species are the 

 irregular shape of the columns, their frequent bifurcation 

 ■and confluence, and the regularity of the intercolumnar space. 



As all the spcimens at command are fragments, it is im- 

 possible to determine what may have been the shape of the 

 organism in its aggregate or compound form. 



Locality and Mode of Occurrence. 



The locality where Dr. Chewings discovered the fossils 

 described in this paper was near the eastern end of the South 

 MacDonnell Ranges, on the north side of the mail road from 

 Alice Springs to Arltunga, midway between Mount Benstead 

 and Love's Creek station. 



