BY W. S. DUN, W. H. RANDS, AND PROFESSOR DAVID. 307 



therefore, nearly twice that of the C oscinodiscus figured by us. 

 The greatest transverse outside diameter, measured at right 

 angles to the long axis of the figure of the form shown on PL xix., 

 fig. 1, is 0-025 mm., and the greatest internal measurement, in 

 the same direction, is about 018 mm. There seems to be a 

 distinct wall present inside the hexagonal network. This wall is 

 about 0-003 mm. thick, and at first sight appears to be perforated, 

 but it is doubtful whether it really is so. The thickness of the 

 wall at the ends (the girdle [?]) is about 0001 6 mm. 



As regards the mineral constitution of the comparatively thick 

 wall, it is seen to be chiefly calcite, when examined in polarised 

 light. 



That the sections figured are diagonals of discs cut approxi- 

 mately at right angles to the valve surfaces of the disc, is 

 rendered probable by the occasional occurrence of associated circu- 

 lar forms, which, in one case at least, agree in measurement exactly 

 with the form figured (PI. xviii., flg. 1). These circular forms also 

 exhibit in some cases a hexagonal mesh-work. Blackish opaque 

 spherical bodies are visible in most of the specimens of this type of 

 Diatom (?). Some of these are figured on PL xix., fig. 1. They 

 vary in diameter from about 005 to 0*01 mm. 



(b) Kndiolarla. — Complete shells are rare, but fragments of 

 radiolarian skeletons are plentiful. One of the most complete 

 forms observed is figured by us on PL xviii., fig. 3, and PL xix., 

 lig. 3. It consists of three concentric shells, united by radiating 

 cross-bars. 



The extreme diameter of the cortical shell (outside measurement) 

 is 0-11 mm. The extreme diameter of the middle shell (outer 

 medullary test [?]) is 0-045 mm., and that of the inner medullary 

 shell 0-0225 mm. This genus agrees fairly well in shape and size 

 with the form figured by Dr. Hinde (oj). cit.) from Port Darwin 

 as Astrophacibs. 



(c) Infusoria — TiiUinnus sp. — The form figured belongs to a 

 type which is very abundant and characteristic in this rock. It 

 resembles a .syringe in shape. The lorica is formed of a delicate 

 black hexagonal mesh-work. Its greatest length, as preserved, 



