249 
Obolella, f'P- 
(Plate XXV., tigs. 4-0.) 
Obs. — It is often a difficult task, in dealing witli tliese 
old organisms, particularly when imperfect, to determine how 
far difference in outline is to be allowea to have weight in 
varietal significance. Associated wim Obolella wirrial pen.<is 
are a few examples differing from the latter by their ovate 
flask-shaped outline, accuminating towards the umbo, and 
swelling out towards the front : the sculpture appears to be 
similar to that of 0. irirrialpenx'tx. 
In form this rarer shell is clearly allied to the little 
0. gemma, Billings,"^ of the North American Middle Cam- 
brian, but is very much larger than the latter. 
I anticipate it will ultimately prove to be specifically dis- 
tinct from (). irirrial pensis, but as the amount of material is 
limited I content myself by suggesting that it be called O. 
wir rial pen sis, var. calceoloides. 
Genus Orthis, Dolman, 1828. 
(Kongl. Vet. Acad. Handlingar, 1827 (1828), p. 96.) 
Orthis (?) tatei, sp. nor. 
(Plate XXV., figs. 7 and 8.) 
Sp. Char. — Pedicle valve, dorsal margin comparatively 
straight ; ventral and lateral margins rounded, the former 
non-emarginate ; umbo small, depressed : surface in the me- 
dian line moderately convex, the wings rather flattened ; sculp- 
ture consisting of numerous, thick, sometimes bifurcating, ra- 
dating costae, which die out, or are only faintly perceptible 
on the wings or towards the lateral margins of the valves, the 
surface on these portions being also crossed by very fine con- 
centric lines ; by the prominence of two or three costae on each 
side of the middle, a flattened space, taking the place of a 
sulcus, is marked off. 
Obs. — In the absence of internal features, 1 am bv no 
means confident in the generic reference of this fossil, but in 
all probability it is an Orthis. The specimens present a very 
analogous appearance to one of the late ]\Ir. Thomas David- 
son's figures of 0. lenticidaris, Wahl.,t from the Dolgelly 
Group of the Upper Lingula Flags of Wales. 
The shell is named in honour of the late Professor R. 
Tate, who practically laid the foundation for palaeontological 
study in South Australia. 
* Walcott— Bull. r.S. Geol. Snrvev. No. 80, 1886, n. 116 
t. 10, figs. 2 and 2a. 
t Davidson — Mon. Brit. Foss*;. lirach.. jjart vii.. No. .3. 1869, 
pi. xxxiii., figs. 27-28a. 
