324 



Genus AMUSSIUM (Klein), Megerle von MiiUfeldt. 

 [Ges. Naturf. Fr. Berlin, Magazin, 1811, p. 59.] 



Shell almost orbicular, depressed,. auriculse small, equal in size; 

 valves smooth on the exterior, but having radiating ribs in the 

 interior, which is the principal differentiating feature of the genus ; 

 ventral border not plicated. 



Of the two species mentioned by Megerle von Muhlfeldt the 

 following is selected as the type of the genus. 



Type. — Ostrea ohliterata, Linnaeus. 



Amussium zitteli, Hutton (sp.). 



ISbo. Pecten, sp., Zittel, Eeise der Novara, Palaontologie, Bd. i. Abth. ii. 



p. 63, taf. ix. figs. \b and 3. 

 1873. Pecten zitteli, Hutton, Cat. Tert. Moll. N.Z. p. 32. 

 1880. Amussitim atkinsoni, Johnston, Pap. Boy. Soc. Tas. 1879, p. 41. 

 1886. Pecten zitteli, Tate, Trans. Eoy. Soc. South Aust. vol. viii. p. 115, 



pi. vii. figs. Za-c. 

 1893. Pecten zitteli, Tate and Dennant, id. vol. xvii. pt. 1, p. 224. 

 1895. AniKssium zitteli, Tate and Dennant, id. vol. xix. pt. 1, p. 112. 



Shell small, interior smooth, shining and furnished with from 

 nine to eleven costas which are truncated near the margin ; left 

 valve concentrically striated, auriculse unequal ; right valve striate- 

 reticulate, or ridged, but the exterior ornament is very variable. 

 Professor Tate,' in detailing this peculiarity, says that "the right 

 valve varies very much in respect of the number and thickness 

 of the radial and concentric threads ; usually the radial threads are 

 stouter than the raised concentric lines, but this form merges on 

 the one hand into a fenestrated ornament, and on the other to 

 one in which the radial ridges are very prominent and minutely 

 scaly." The posterior auricle of the right valve is larger than 

 the anterior ; it is triangular and cancellate. 



It is allied to A. sqiiamula, Lamarck, of the Parisian Eocene, but 

 the latter is devoid of conspicuous reticulate ornament on the 

 exterior, and is relatively longer. 



Dimensions. — Height 8 mm. ; length 9 mm. 



Form and Loc. — Eocene : Muddy Creek, Victoria. 



L. 9876. Several examples of both valves. Purchased. 



1 Trans. Eoy. Soc. South Aust. vol. viii. 1886, p. 115. 



