226 Proceedings of the Royal Society of Victoria. 



minutely spinulose near the beak. Middle and anterior portion 

 of the valve bearing narrow-rounded undulating transverse 

 ridges ; the middle portion or that immediately anterior to the 

 siphonal ridge being ci-ossed by what appear to be impressed 

 lines, number variable, generally about ten, frequently less, 

 radiating from the beak to the ventral margin, shows the ripple- 

 like ridges l>roken up into quadrangular nodes. 



Diinetisions. — Average of a number of specimens, antero- 

 posterior diameter, 39 mm.; umbo-ventral diameter, 37 mm.; 

 thickness through one valve, 11 "5 mm.; thickness of shell, 3 mm. 

 The largest example of the species I have yet seen has the 

 following dimensions, antero-posterior diameter, 55 mm.; umbo- 

 ventral diametei', 49 mm. ; tliickness of sliell, 3'5 mm. 



Locality. — Abundant in the Lower Eocene calcareous sands, 

 Moorabool Valley, near Maude. 



Observations. — This species may at first sight be confounded 

 with T. semiundulata, McCoy, to which it is closely related, l)ut 

 upon examination may be easily distinguished fnjm Sir F. 

 McCoy's species by its much thicker*, more solid, and more 

 regularly convex shell, not .so attenuate posteriorly, by the 

 greater angle the posterior margin makes with the hinge line, the 

 absence of flattening of the posterior slope, the straighter ventral 

 margin, the smaller number of posterior radial ribs, and the less 

 crowded transverse ridges. From our other fossil .species of tbis 

 genus, namely, T. howitti, McCoy, T. acuticostata, McCoy, and 

 T. tulmlifera.^ Tate, it is still more re;idily sepai'able, as the first 

 two have, like the recent species, radial ribbing only, while the 

 third is a minute shell with well developed tubular projections 

 on the transverse ridges as well as on the radial ril)s. 



The first examples of this species that came under my notice 

 were in the collection of the Rev. A. W. Cress well, M.A., of 

 Camberwell, who had t)btained his specimens from the Maude 

 district. Subsequently I had an opportunity of visiting this 

 district in company with Mr. T. S. Hall, and was able to collect 

 a large series of specimens. 



Species name in comjiliment to Professor Ivaljih Tate of the 

 Adelaide University. 



