306 



Dimya dissimilis, Tate. 



1886. Dimya dissimilis, Tate, Trans. Eoy. Soc. South Aiist. vol. viii. p. 100, 



pi. iii. figs. 9a-c. 

 1893. Dimya dissimilis, Tate and Dennant, id. vol. xvii. pt. 1, p. 224. 

 1895. Dimya dissimilis, Tate and Dennant, id. vol. xis. pt. 1, p. 112. 



Attached valve largely scarred by the broad area of attachment 

 in the neighbourhood of the umbo, remainder of surface plicated, 

 the ridges extending to the margin, they are scaly, undulating, and 

 irregular ; interior extensively occupied by the circumscribed white 

 area in which the muscle-marks are situated, which is flanked 

 on either side by a short row of elongate denticles; hinge-pit 

 triangular and transversely striated. Unattached valve flat, having 

 a prominent umbo, from which the growth-lines gradually increase 

 in vigour until they undulate and become plicated, forming radial, 

 imbricating lamellae, much as in common species of Chama; muscle- 

 scars as in opposing valve. 



Dimensions (attached valve). — Height 21mm.; length 17 mm. 



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



L. 4806. Several examples of both valves. 



Presented hy John Dennant, Esq. 



L. 9838. A series of both valves showing stages of growth. 



Purchased. 



Dimya sigillata, Tate. 



1886. Dimya siyillata, Tate, Trans. Eoy. Soc. South Aust. vol. viii. p. 100, 

 pi. viii. figs. 9ia-h. 



This differs principally from D. dissimilis in having much finer 

 ornament on the attached valve, which latter is usually more 

 convex, and in having conspicuous ridges or riblets in the interior, 

 radiating from the circumscribed area to the pallial line. 



Dimensions (attached valve). — Height 8-5 mm. ; length 6'5 mm. 



Form, and Loc. — Eocene : Aldinga, South Australia. 



L. 10030. Several examples of both valves. Purchased. 



