vex, radiately ribbed with about 36 rounded subgranular ribs, 

 with smaller ones sometimes between ; finely, regularly, and 

 closely concentrically Urate ; umbones small, rounded, can- 

 cellate ; inside snowy white and polished ; ligamental fossa 

 trigonal, minute ; teeth 22-24 ; margins thickened, flattened, 

 polished, within which the shell is not shining, but is radiately 

 striate. North Coast, W. F. Petterd. There is much reason 

 to doubt if this rare shell, of which few specimens are ever 

 found out of very deep water, is not identical with the common 

 fossil of Australian tertiaries L. deciissata. 



No. 77. Mttilus latus Lam, nov. rar ? M.t. late rotundata et postice 

 obtuit angulata,valdecompressa,tenui, polita, tcnuiter regulariter sulcata, et 

 irregulariter lineis incrcmenti, et tenuissime radiatlm striata, epidermide 

 intense olivacea, duobus lineis latis lutcis ah umbonibus marginem versus 

 ornata, ad ligamentum elcgantcr rufo-fulvo nebulosa, umbonibus parvis, acutis, 

 incurvis,lcevis, albis, marginibusacutissimis. 



There are many species of Mytilus recorded as Tasmanian, 

 and this does not agree with the description of any of them. 

 Its peculiar characters are its very compressed falcate habit, 

 and its brilliantly shining olive epidermis, with the yellowish 

 brown broad arched line proceeding from the umbones along 

 the margins. In Dr. Cox's collection the shell marked M. 

 dunkeri has an olive epidermis, but it is a tumid solid shell. 

 Reeve's figures of M. dunkeri are evidently from worn speci- 

 mens. M. dunkeri is an American shell wrongly called 

 Australian by Reeve, M. rostratus is a different species. 

 I do not regard it as more than a variety, nor are 

 the variations between the species greater than those to 

 which M. edulis of the European seas is subject, and which 

 has received a dozen names. That shell has also an olive 

 epidermis, but is a much more dull and tumid shell. 



No. 78. Mttilus crassus. v.s. M.t. nitente, subquadrata, medio 

 angustata,subg ibbosa, postice rotundata et subattenuata, valde tumida, et oblique 

 conspiru6 unicostata, costis in umbonibus subspiral iter desinentibus ; epider- 

 mide intense badia ; paucis cappUis long is, cornels, in disc is albis, convexis, 

 rotundatis, radicatis armata ; lineis increment, irregvlaribus elevatis, con- 

 spicuis ; marginibus epidermvle fulva, nitente, indutis ; umbonibus margara- 

 taceis, glabmtis ; fossula producta, umbonibus parum excedenti ; pagina 

 interna cameo-alba, impressione pallii et musculari purpurascente, conspicua : 

 ligamento longo conspicuo. Lung. 21, lat. 11, diam. 2 valviacouj. 13. 



This dwarfed Mytilus is easily distinguished by its tumid 

 subgibbose form, and the inordinate thickness of the shell 

 when the valves are conjoined. It has a rugose, shining 

 lacquer-like epidermis of intense brown color, on which are a 

 few wart-like discs supporting long stout bristle-like hairs. It 

 has also a conspicuous rounded ridge or rib on each valve, 

 which curves almost to a spiral at the umbo. 



Rare at Circular Head, and abundant at Adventure Bay, 

 W. F. Petterd. 



