461 
towards the ventral portion, obliquely rounded, with a larger and better developed 
posterior ear than in the left valve ; anterior margin rounded ; anterior ear more or less 
triangular, reposing completely in the insinuation of the anterior margin of the left 
valve, separated from the body of its own valve by a deep byssal sinus ; beak small, but 
sharp and prominent. Hinge-line of both valves short, but longest in the right ; no 
tooth visible in the interior of the right valve. Both valves are crossed by fine radiating 
stria) which give rise to a minute cancellation; in the left valve the striae are more 
apparent below the beak, and die out on the body of the shell ; in the right valve they 
are of a fluctuating or wavy character, and the concentric laminae become frill-like; 
surface highly polished. 
Attcella hugltenJenensis is undoubtedly allied to two types of the genus, 
A. Fallasii, Keyserliug,* * * § and A. crassicollis, Keys.f In imssessing the obliquity and 
short hinge-line, it resembles the former ; the loft valve has the general form of the 
latter species and a similar much incurved beak, whilst the right valve in all its 
peculiarities is almost identical with that of A. FaUmii. The resemblance of our shell 
to and its intermediate position between the two sqrecies in question is very remark- 
able. A. Imyhendenemis is also allied to the Indian Cretaceous species A. parva, 
Stoliczka, J but the left valve in the former is more inoceramiform than in the latter, 
and more oblique. 
In A. speluncaria, Schlotheim,§ there are radiating stripe, but our species is less 
deltoid and more regular, and there is no inflection of the ventral margin. 
A. Sammanni, Goldfuss,|| from the Zechstein of Soharzfeld, is a much more 
slender shell than the Australian species, less convex, and more elongate from the beaks 
to the ventral margin. Another species, A. cmtcasica, Abichjlf possesses fine radiating 
striae, to say nothing of the larger ear in the rigjit valve, a mote pointed and prominent 
nmbo in the left, and a generally different outline to the valves. There appears to be 
at least one very interesting British example of Aticella, the A. gryplimoides, J. de C. 
Sowerby, sp.,** * * §§ but it has a much larger umbo in the left valve, and the general characters 
of the right are quite different. 
The last species with which I am able to compare A, liugliendenensis is the 
American Cretaceous form of A. Pioahii, Gabb,tf a very gibbous and thick shell through 
the valves, quite distinct from the Australian. It is not related to A. plicata, Zittel,++ 
which differs in form, and has coarse concentric corrugations over the valves. 
Aucella liugliendenensis was no doubt a very abundant species, and probably 
gregarious, “ masses of them occurring together, forming a compact and dense 
argillaceous limostone.”§§ It was equally variable, for in some the radiating strise only 
predominate ; in others a reticulation caused by the presence of transverse concentric 
lines is the main feature. Two or three of the radiating ribs sometimes become very 
much larger and promi lent. The smaller valve has at times an almost Anomia-\\kQ 
appearance, sometimes a little gnarled, and corrugated by three or four concentric 
ridges and correspoudiug depressions. In individuals of more advanced age the 
* Reise in d-is Petschora-LancI, p. 299, t. IG, f. 1-7. 
t Uiid., p. 300, t. 16, f. 9 and 12. 
+ Pal. Indica (Cret. Fauna), 1871, iii., fas. 5-8, p. 404, t. 33, f. 2 and 3. 
§ Sec Geinitz, Dyas, t. 14, f, 5-6. 
WMytilus, Petrefacta GeraianisB, ii., p. 168, t. 138, f. 4; Aucella, Geinitz, Dyas., p. 72, t. 14, f. 85. 
IT Zeitsch. deutschen Geol. Gesellsoh., 1851, iii., p. 31, t. 2, f. 1. 
** Trans. Geol. Soc., iv., t. ii., f. 3, 
ft Pal. California, ii., t. 32, f. 92. 
Jt Reise Oesterr. Fregatte “ Novarra,” 1857-59, Geol. Theil, Band I., 2 Abth., 1865, p. 32, t. 8, f. ia-c. 
§§ Etheridge, Quart. Journ. Geol. Soc., 1872, xxviii., p. 346. 
