550 F. Chapman & E. W. Slceats — Fossil Hydroid Remains. 



V. — On the Discovery of Fossil Hydroid Remains op the Order 



Calyptoblastea in the Paleozoic of Victoria, Australia. 



(PLATE XV.) 



By Frederick Chapman, A.L.S., Palaeontologist to the National Museum, 

 Melbourne, and Professor Ernest W. Skeats, D.Sc, A.R.C.S., F.G.S., 

 University of Melbourne. 



SINCE no undoubted fossil remains of this group of hydroids have 

 been previously recorded, with the exception of possible forms 

 indicated by Ruedemann but placed by him with the Graptolites, it 

 is thought that a few brief notes on a recent discovery in Victoria 

 may be acceptable to readers of this Magazine. A description of 

 the fossils by one of us (F. C.) will appear in the Proc. Roy. Soc. 

 Victoria, while a description of the stratigraphy of the area will 

 be given by the other author (E. W. S.) 



Rocks in which the Fossils occur. 



The fossils are found in a black shale about 2 miles north-east of 

 North Monegetta and 2-g- miles south-east of Romsey railway stations 

 and about 40 miles north of Melbourne. The black shale occurs as 

 vertical outcrops in Deep Creek, striking, N. 20° E., interbedded with 

 black cherts and in conformable contact with Heathcotian (Cambrian) 

 diabase which forms Hurst's Hill east of Deep Creek. The fossils 

 are associated with a Brachiopod^m^reta antipodum, Chapm., which 

 suggests a horizon low down in the basal Ordovician, but somewhat 

 similar branching forms occur with Dinesusida and other trilobite 

 remains of probably Cambrian age near Heathcote, about 30 miles 

 further north. 



Condition of Fossils. 



The remains of the hydrosome are seen as a silvery- white film on 

 the dark slate. In the case of Mastigograptus this film is very 

 tenuous and seems to disappear rapidly into the slaty surface, 

 though under a lens the thecal growth can be seen extended for quite 

 a distance. The shape of the aperture of the cups of both 

 hydrothecse and gonothecse is distinct. 



Definition and Relationships. 



Comparing these Palaeozoic fossils with living hydroids, two 

 generic forms seem to be closely related to living genera, and are 

 accordingly named Archceocryptolaria {A. slceatsi) and Archceolafoea 

 {A. recta and A. longicornis). Arcliceocryptolaria resembles in its 

 long, cylindrical hydrothecse Cryptolaria angulata, Bale, a living 

 form found in the Great Australian Bight at 100 fathoms. 

 Archceolafoea is compared with the living Lafoea fruticosa, Sars. 

 Mastigograptus was described by Ruedemann from the Htica Slate 

 of Trenton, New York (Middle Ordovician). M. monegetta shows 

 less tendency to branch than in M. temiiramosus of Ruedemann. 



EXPLANATION OF PLATE XV. 

 Fig. 1. — Archceocryjitolaria skeatsi, Chapm. 

 ,, 2. — A. longicornis, Ch. 

 ,, 3. — A. recta, Ch. 

 ,, 4. — Mastigograptus monegetta, Ch. 

 From black shale in the basal Ordovician near North Monegetta, 40 miles 

 north of Melbourne, Victoria. Figures slightly enlarged. 



