Park. — The Lower Mesozoic Bocks of Neiv Zealand. 397 



Eocky Gully fossiliferous shell beds is beyond all doubt, and, 

 with respect to the diverse opinions and evidence quoted 

 above, we can only conclude that a misunderstanding arose 

 between Sir Julius von Haast and Professor McCoy in the 

 transmission and description of the fossils. 



Briefly, we find that the plant beds are held to be Triassic 

 or Jurassic ; while the overlying marine beds, on the shell 

 determinations of Professor McCoy, are Carboniferous, or, ac- 

 cording to the saurian determinations of Sir James Hector, 

 Triassic. 



(c.) Trigonia Beds. — In most places these are characterized 

 by the presence of Trigonia, Estheria mimita, Edmondia, Am- 

 monites (sp. not determined), a nautiloid shell, Murchisonia, 

 Comdaria, and Spirigera (Athyris) wreyi, Zittel. 



These beds are well developed in Well's Creek, Eighty- 

 Valley and Mount Heslington sections. In the Shaw's Bay 

 eight Valley, and on southern slopes of Mount Heslington, 

 Nelson, in Shaw Bay, and many parts of Hokonui Hills. 



(d.) Mytilus problematicus and Monotis salinaria Beds. — 

 These beds generally consist of a compact mass of Mytilus or 

 Monotis, to the exclusion of all other forms. 



The Mytilus beds attain a great thickness in Eighty-eight 

 section the My tikis bed is composed principally of a con- 

 fused mass of oyster-shells. At Nelson the cast of a large 

 Gryphaea is occasionally found in the Mytilus beds. 



Monotis salinaria, Zittel, is present at Mount Heslington, 

 French Pass, Okuku (in Canterbury), and many parts of Hoko- 

 nuis. It IS absent in the Shaw's Bay section. In the Hokonui 

 sections Monotis seems to take the place of the Mytilus, so 

 abundant in the Nelson Trias ; and throughout that region 

 the Monotis beds follow the Trigonia beds, as do the Mytilus 

 beds in Nelson and southern Otago. 



(a.) Clavigera Beds. — These beds everywhere form the 

 close of the Trias. At Shaw's Bay they contain only two 

 distinct shell-forms — namely, an Athyris-Wke form and Spiri- 

 ferina. 



The Athyris is rather an unusual form. It is smooth, bi- 

 sulcate, has a long slightly curved hinge-line, and possesses 

 the habit of a spirifer rather than that of an Athyris. It cor- 

 responds closely with the Clavigera of Hector, which is a sub- 

 genus of Athyris created to include this unusual form.* 



The Spiriferina possesses a straight hinge-line with comb- 

 like dentition, and is the sub-genus Rastelligera of Hector. f 



In Well's Creek, Nelson, the Athyris horizon contains 

 several species of Spiriferina (including Rastelligera, which is 



* Trans. N.Z. lust., vol. xi., 1878, p. 537. 

 t Loc. cit., p. 537. 



