266 DE. C. T. TRECHMAJJN 0> T THE [vol. lxxix, 



impossible. The place of origin of the genus * is a point on which 

 much discussion has taken place with little result, as Gr. Bcehm 

 thinks. 



Aucella plicata Zittel. (PL XVII, figs. 4-8.) 



Description. — Left valve more or less strongly arched, some- 

 times narrow and laterally compressed, the outline being in con- 

 sequence very variable. Beak prominent, rather anteriorly directed, 

 projecting above the hinge-line and more or less strongly bent 

 over it. The anterior ear is rounded and arched. A narrow sulcus 

 or furrow in some examples passes from in front of and below 

 the beak to the lower posterior margin, which is generally some- 

 what produced. In some examples the surface is almost smooth, 

 except for very faint, close-set, rather foliaceous growth-lines. In 

 others these are more prominent and widely spaced, while radial 

 ridges may be prominently developed, giving a reticulated orna- 

 mentation to a part or all of the shell-surface. The shell of both 

 valves in larger examples becomes wavy and irregular towards the 

 lower and posterior margin. The surface of the right valve is 

 sometimes rather arched, but generally well-rounded ; the anterior 

 auricle is well developed, and the beak small. Growth-lines are 

 more or less widely spaced and irregular ; but the radial ridges are 

 generally weak, giving a faintly reticulated ornament to part of 

 the surface. 



Dimensions. — Left valve : height=21— 27 mm., length =: 16- 

 22mm.; depth = 10-15 mm. Bight valve : height= 20-22 mm. ; 

 length = 20 mm. ; depth = 6-8 mm. 



Locality. — Kohai Point, Kawhia, in calcareous shales with 

 Inoceramus haasti; Oxfordian, or rather later. Several examples, 

 both complete and broken, were collected. 



Remarks. — The specimens are individually very variable, sug- 

 gesting distinct species. The differences, however, result from the 

 degree of inflation and arching of the beaks, the absence or 

 presence of a furrow on the left valve, and the degree of folia- 

 tion of the growth-lines and strength of the radial ribs with 

 consequent reticulation of the surface. An}^ attempt to apply 

 varietal names to a series of these shells would only lead to an 

 unnecessary multiplication of trivial terms. 



A comparison of this species with Aucella Iwgliendensis 

 B. Etheridge fil., 2 of which I possess a slab with numerous speci- 

 mens from Hughenden (Queensland), has been made, but the two 

 forms do not seem to be closely related. The left valve of the 

 Australian species is more strongly arcuate, and, although it bears 

 a reticulate ornamentation, the species seems to be a much less 

 variable one. 



1 J. F. Pompeckj, ' Aucellen im Frankischen Jura' Neues Jahrb. vol. i 

 (1901) p, 32; ' Ueber Aucellen & Aucellen-ahnliche Formen ' ibid. Beilage- 

 Band xir (1901) p. 319. 



2 ' Geology & Paleontology of Queensland ' 1892, p. 460 & pi. xxv, figs. 1-6, 



