853 



1888. Tiigonia seniiundidata, Johnston, Geol. Tasmania, p. 235, pi. xxix. 



fig. 5. 

 1893. Triffoiiia semiundulata, Tate and Dennant, Trans. Roy. Soc. South 



Aust. vol. xvii. pt. 1, p. 224. 

 1896. Trigonia semiundulata, Pritchard, Proc. Roy. Soc. Vict. vol. viii. n.s. 



p. 131. 



Shell abruptly trimcated and crenulated posteriori)' ; umbones 

 near the anterior margin, which, in consequence, is short ; external 

 ornament consisting of prominent, curved, radiating, and occa- 

 sionally granulate costae, which occupy nearly one-half of the 

 surface posteriorly, and abruptly terminate against a number of 

 rather smaller curved ridges parallel to the ventral margin ; these 

 latter also bear some inconspicuous radiating costas about the 

 middle of the shell, which produce granulations at the points 

 of intersection with the curved ridges alluded to. 



Bimemions. — Height 88 mm. ; length 46 mm. 



Form, and Loc. — Eocene : Tasmania and Victoria. 



83996. Portion of right valve ; from Table Cape. Purchased. 



L. 4838. Two right valves ; from Muddy Creek. 



Presented hy John Dennant, Esq. 

 L. 6599. Examples of both valves, one of the neanic stage 

 of growth, and the other of the ephebic ; from Muddy Creek. 



Purchased. 



L. 9847. Specimen of the adult, both valves ; from Muddy 



Creek. Purchased. 



Trigonia tatei, Pritchard. 



1895. Trigonia tatei, Pritchard, Proc. Roy. Soc. Vict. n.s. vol. vii. p. 225, 

 pi. xii. figs. 1-3. 



Closely related to T. semiundulata, fi-om which it differs in being 

 more solid, regularly convex, not so elongate posteriorly, and 

 consequently the shell is proportionately higher; there are fewer 

 posterior radial costte on the surface, whilst the transverse ridges 

 are bolder. 



Dimensions. — Height 37 mm. ; length 40 mm. 



Form, and Loc. — Eocene : Maude, Victoria. 



L. 10024. Eight valve of the adult. Purchased. 



