92 Proceedings of the Royal Society of Victoria. 



seems to me that we can proceed to an extreme form, for which 

 it seems advisable to propose at least a vainetal name. 



Variety, gpanosa, var. nov. (PI. XV., Fig, 5). 



In shape similar to T. semiundulata, but proportionately a little 

 shorter in its antero-posterior diameter, with eight distinct radial 

 ribs on the posterior slope and three fainter spinose beginnings 

 post-doi'sally, anteriorly the undulating ridges are completely 

 broken up into triangular nodes right up to the anterior n)argin, 

 and so deeply impressed are the sulci that the shell has rather 

 the appearance of being radially nodosely ribbed here also, there 

 being 18 radiations on this portion, while looking at it from the 

 point of view of undulations the number is about 25, and further 

 apart than in the usual type, hence the granules or nodes are 

 rather coai'ser than those usually developed. 



Dimensions. — Antero-posterior diameter, 25 mm.; unilx)- 

 ventral diameter, 23 mm.; thickness through one valve, 7 mm. 



Locality. — Lower beds of the Spring Creek series or Bird Rock 

 Bluff, near Geelong. Jan Jukian, — Eocene. 



A^ariety, lutosa, var. nov. (PI. XV., Figs. 6, 7). 



The next form for considei-ation is that commonly occurring at 

 Muddy Ci'eek, which is a veiy distinct variation from the typical 

 form of the species. The .shell is more oblong owing to a greater 

 posterior attenuation, and is much narrower at the posterior end, 

 the posterior area is more depressed, and the anterior area is 

 rather more tumid and more regularly convex ; the anterior 

 undulations are coarser, less numerous, more regular, and do not 

 ascend so rapidly; while the radial sulci are usually very faint, 

 sometimes almost absent, or showing somewhat as a fimbriation 

 of the ventral aspect of the concentric undulations, occasionally 

 distinct on the upper half of the shell, and then very closely 

 packed, considerably closer than in T. undulata, and then also 

 apparently restricted to portion of the ventral slope and the 

 interspace between the undulations. 



Dimensions. — Antero-posterior diameter, 40 mm. ; uml)o- 

 ventral diameter, 33 ram.; length of posterior, 22 mm. Otlier 

 specimens range about 38 by 31-5 by 20; 36 by 30 by 18; 35 by 



