]46 MATTHEW ON CAMBRIAN 



been injected with silica. To this mode of replacement also we owe the preservation of 

 some of the delicate setee which clothed the stem. 



This aud Bidhotrephis antiqaa which occurs with it, are the two oldest organisms of 

 the Cambrian rocks in Acadia. 



HYDEOCYTIUM. 



Among the microscopic forms in the Cambrian shales are some minute oral bodies 

 which by their black color are shown to have been composed of dense organic matter. 

 They appear to have been held together by a strong epidermis, as the contents are often 

 found shrunken together so as to leave irregular cavities near the centre. Until better 

 known, they may be referred to the above confervoid genus. 



HyDROCYTIUM (?) SILICULA, n. sp. (PI. VI, fig. 2.) 



Minute, oval bodies, with a strong cuticle, and having a pedicel-like knob at one end. 



Size. — Length, J mm. ; width, \ mm. 



Horizon and Locality. — In soft green shale of 1 6 of the St. John group. 



These organisms are not abundant ; they are large enough to be visible to the naked 

 eye. Other detached and scattered minute black bodies are more common. These may 

 be the spore cases of algae ; they are intensely black, and gave tuberculated surfaces ; they 

 are usually globular or oval in form. Two of these are figured in the accompanying 

 plates. (Plate VI, fig. 3.) 



MICROPHYCUS, n. gen. 

 MiCROPHYCUS CATENATUS, n. sp. (PI. V, figs. 6a-6.) 



Minute, reticulated organism, forming a net-like expansion on the sea bottom ; with 

 enlargements or nodes at intervals. The connecting threads are nodulose, composed 

 apparently of chains of single cells. The nodes are tuberculated as though they consisted 

 of an aggregation of cells. The cells are filled with a dense organic matter, appearing of 

 a black color in contrast with the fine, greenish grey shale in which they are imbedded. 



Size. — The nodes have a diameter of about tV mm., and the connecting threads a 

 length of about | mm. 



Horizon and Locality. — In the fine grey shales of Div. 1 b i*, St. John group at 

 Ratcliffs millstream. 



This microscopic alga is a most interesting object. The horizon of the Cambrian 

 where it is found is the same as that which in the northern basin (Long Eeach) is 

 sandy and coarse and comparatively barren. Here it is a fine soft shale, which, to judge 

 from the perfect condition of the most delicate sponges and the erect position of many of 

 them in the shale, was deposited in the still waters of a sheltered bay. Through this 

 mud, and even into the tissues of the sponges, this alga extended, forming an intricate net- 

 work. 



