Tertlary.l PALEONTOLOGY OF VICTORIA. [M^llusca. 



Plate XXV., Figs. 1-15. 

 PLEUROTOMARIA TERTIARIA (McCoy). 



[Genus PLEUEOTOJIARIA (Def.). (Sub.-kingd. MoUusca. Class Gasteropoda. Order 

 Scutibraudiiata. Fam. Haliotida?.) 



Gen. Char. — ^Usually pyramidal, trochiform, more rarely globose, or depressed ; aperture 

 usually wider than lonpr, with a deep narrow respiratory slit in the outer lip, leaving a defined, 

 linear, spiral band, marked by retroflexed striae along each whorl of the spire ; surface usually 

 marked by striie archmg backwards towards the band ; columella simple, a little thickened in 

 front, with or without umbilicus. 



The trochiform species differ from Trochus by the sinus and band.] 



Description. — Shell lare^'e, trochiform, apical anp;le 67° ; whorls flat, or very 

 slightly convex ; base moderately convex, with (?) a small umbilicus ; band of moderate 

 width in the middle of each whorl, slig-htly depressed. Surface with sub-equal 

 prominent thread-like .spiral striae, rather less than their thickness apart (about 10 

 or 11 above, and the same number below the band), about 3 slig-htly smaller on the 

 band, reticulated by arched stritC, narrower, but nearly as prominent as the spiral 

 stri«, and slightly further apart. Length about 2 inches 9 lines ; proportional width, 

 -j%% ; length of last whorl, ^j^^. 



If this fossil had been found alone, or if the other fossils found 

 Math it had not proved the Upper Miocene Tertiary age of the 

 stratum, it would in all probal)ility deceive any geologist into the 

 belief of its affording evidence of Oolitic strata. 



The genus Pleurotomaria, like Trigonia, is a most abundant one 

 in all the Mesozoic marine formations, but, like Trigonia, also has 

 hitherto been remai'kable for its sudden, almost complete, disap- 

 pearance at the close of the Cretaceous period, and being so nearly 

 absent in the well-searched Tertiary formations of Europe, Asia, 

 and America, that only two examples of Tertiary age seem to have 

 occurred to any observers, viz., the P. Sismondai, found by 

 Goldfuss at Biinde, and the P. concavn found by Deshayes in the 

 Paris basin. So rare are these occurrences, however, that neither 

 myself nor I believe any living palaeontologist has seen a trace of 

 them. The genus reappears in our recent seas, where it is repre- 

 sented by two such excessively rare species that only one or two 

 examples have been found. Our Victorian fossil is almost inter- 

 mediate in character between the two living ones, having the large 

 size, more elevated spire, and more numerous and flatter whorls of 



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