LOWEH CRBTACKOU.S FOSSILS — ETHERIDCJK. 321 



An interesting point (occurs in coiuiection witli the relation of 

 these sliells to O.rytomti rocktfootlfusis, mihi." The shorter and 

 broadei- examples closely resemble this, but the costal in the latter 

 are so much less in number. Before i-elegating 0. rockivoodensis 

 to the position of a synonym of j\l. rorbii'iisis it will be necessary 

 to see the interior of the former ; sliould the two articuli agree, 

 and my assumption tliat the present fossils are a dwarf race of 

 the latter, it will be useful to distinguish them by using the name 

 of the fii'st in a varietal sense for the present fossils. 



(reuns AucELLA, Keyserliuy, 1<S46. 

 (Reise in das Petschora Land, 1846, p. 297). 



AUOELLA HUGHENDENENSIS, Etheviiliji'. 



(Plate Iviii. ; PI. Ixi., figs. 7-12). 



Avicitla hm/hendeu&nsis, Etheridge, Quart. Journ. Geol. Soc, xxviii., 

 lS72,'p. 346, pi. XXV., f. 3. 



Aua'Ua huyheudeitensis, Eth. fil., Mem. R. Soc. S. Austr., ii., 1, 

 1 902, p. 1 4 (/o7' synonomy). 



Obs. — Foremost amongst the specimens of this collection is a 

 very beautiful weathered example of this species, by far the finest 

 group I have seen. Although the shell is now well known, other 

 and smaller specimens reveal some points of structure not hitherto 

 noticed. 



The group (PI. Iviii.) displays to great perfection both valves, 

 some in apposition. Amongst other notable points are the size 

 attained, gradual fading away of the delicate costse on the left 

 valve from the umbonal region downwards, and the oblique fan- 

 like outline of the right valve. 



From the smaller specimens already referred to we learn that 

 the small triangular auricle of the right valve was in some cases 

 received (PI. Ixi., fig. 10) in an anterior inflection of the cardinal mar- 

 gin of the right valve Another specimen displays the central and 

 posterior portions of the cardinal margin of the left valve (PI. Ixi., 

 fig. 11) as a broad sub-triangular concave area, but without a 

 chondrophore ; the cardinal margin of the right valve posterior to 

 the umbo is thickened, but without forming a defined area. 

 Another very interesting fact in the right valve is the delicate 



» Etheridge— Geol. Pal. Q'laiul, etc., 1S92, p. 44H, pi. xxiv., f. 15. 



