158 Fossils from Australia. 



flank nearly flat and rounding broadly into the lateral surface ; lateral 

 surface with a depressed area, extending from the beak to middle of 

 inferior margin ; inferior margin straight at middle ; surface marked 

 unevenly with fine striae of growth which are regularly concentric. 



Length 3§ inches ; height y 6 ^ L ; thickness T 3 <j 5 <y L ; apical angle 

 about 142°. — Illawarra. 



Myonia, (nov. gen.) — Shell thick, oblong transverse, inequivalve, ve 



ry inequilateral, much gaping behind. Palleal impression strong, en- 

 tire. Muscular impressions three to each valve ; two anterior and one 

 posterior, all excavate, smaller anterior on the front, posterior on the round- 

 ed carina between the flank and lateral surface. Valves thick. Lateral 

 surface strongly flattened at middle or even concave. — Resembles much 

 Panopsea and Pholadomya, especially Agassiz's Arcomya ; but differs 

 in its entire palleal impression, its second anterior muscle, as well as 

 other characters. 



37. Myonia elongata. — Thick, right valve rather the larger; great- 

 est height half the length; gradually narrowing behind the beak, infe- 

 rior margin just posterior to middle somewhat concave, carina from 

 beak to posterior angle broadly rounded, not bent, flank flat, cardinal area 

 long and circumscribed ; surface strongly marked unevenly with regular 

 concentric striae of growth. — Length 6£ inches ; height -fifo L ; thick- 

 ness T Vcr L; anterior part about half the posterior; apical angle 145°. 

 — Illawarra. 



38. Myonia valida. — General form of the M. elongata : — but greatest 

 height much less than half the length ; flank in cast flattened and dis- 

 tinctly bent near the posterior muscular impression ; muscular impres- 

 sions deeply excavate, and marked with deep vertical sulcations ; palleal 

 impression very strong with slender vermiform erosions extending up- 

 ward from it; also scattered muscular impressions over lateral surface. 



Of the same length with the preceding; but greatest height T 5 x& L; 

 apical angle of cast 128°.—Illaivarra. 



39. Eurydesma elliptica.— Somewhat compressed, and dilated ante- 

 riorly and posteriorly, transverse, right valve largest ; beaks contigu- 

 ous; lateral surface not flattened; surface nearly smooth with occa- 

 sional faint lines of growth and no trace of radiations ; inferior margin 



V ft JT-* tf^fc * • ^ _ 



arcuate.— Length 2§ inches ; height T %% L ; thickness -^ L ; apical an- 

 gle 124°.— Harper's Hill. lJnr 



40. Eurydesma globosa.— Thick, tumid, suborbicular, not transverse, 

 very evenly convex; beaks contiguous; lateral surface every where 

 convex; surface smooth with faint concentric lines of growth and no 

 trace of radiations ; inferior margin and lines of growth, regularly or- 

 biculate.— Length and breadth 1-^ inch ; thickness y 7 ^ L ; apical an- 

 gle 97°. — Harper's Hill ? Illawarra. 



41. Modiolopsis simplex. — Elongate, length rather more than twice 

 the height, very inequilateral, enlarging a little posteriorly; dorsal 

 line horizontal, straight, and rounding into the posterior margin; ob- 

 liquely truncate in front; inferior margin arcuate; lateral surface 

 evenly convex without a depression anteriorly, or a carina posteriorly; 

 surface marked rather faintly with lines of growth, a little uneven. 

 —Length 1£ inch ; height •£& L ; apical angle about 132 .- 

 lllatcarra. 



