197 
sidering that species. The young forms of T. approximatus and T. serra 
(in a peculiar state of preservation) are often difficult to separate T. 
serra, however, being a reclined form, its sicula is usually conspicuous 
and its main stipes are so preserved that they show no tendency to 
become parallel. 
Horizon .—Lower Ordovician and Upper Cambrian. 
The following table represents its approximate vertical range; — 
Fig. 62. —Synoptic table, showing range of T. fruticosus (zone index), T. acclinans, 
T. approximatus, and T. decipiens. 
Other associates in the Bendigo zone are T. clarkei, T. serra^ T. quad~ 
rihrachiatus, T. hryonoides, T. simicis, T. pendens, T. harti, C. rigidus 
var. tenellus, C. magmfi.cus, I), extensus, D. dilatwns, D. latus, G. 
ihureaui ( ?), G. macer (?), P. cf, typais, D. octohrachiatns, which are 
typical of the Lower Ordovician. Its association in the Lancefield 
zone is restricted to a few species including T. decipiens, G. rigidus, var. 
tenellus, Didymograptus ssp. and Bryograptus ssp., an association so 
far only found in Victoria. Below it in the lower part of the Lance¬ 
field zone the genera Bryograptus', Olonograptus and Dictyonema all 
reach the height of their development and are represented by a few 
isolated species in the upper part of the Lancfield and lower part of the 
Bendigo* zone. About subzone L2 of the Lancefield zone a notice¬ 
able change in the character of the thecae occurs, namely, from an 
excess of Bryograptid and Clonograptid types to the typical Tetra- 
graptid and Didyniograptid types of the Lower Ordovician. The writer 
has for many years considered that the greater part of the Lancefield 
zone is at the summit of the Upper Cambrian, and anticipated the find¬ 
ing of such an association as is represented by subzone 2 of the Lance¬ 
field zone^. 
T. approximatus has been found at Dromana, Inglewood, Balnar- 
ring, Bendigo (several localities), Newstead, Boolara, &c., &c. 
‘ Mr. F. Chapman, Hon. Pateontologist to the Oeo. Sur, of Victoria, permits me to state that he has 
identified typical Upper Cambrian Crustacea from the Mansfield chert and phosphate beds. Vide 
“ Phosphate Deposits at iMansfield,” b^ A. M. Howitt, and note on Tetragraptus approximatus and 
T. decipiens. Dull 42, Geol. Surv. Viet. (M.S.). 
