1 ADELACT^ON. 



Shell thick, spirally linear sulcate ; sulci not punctated, close 

 together and varying in prominence, sometimes obliterated. 



M. Cossmann states that this species possesses minute punctations 

 in the spiral sulci, but neither of the specimens in the Museum 

 exhibit that peculiarity, though when seen under the microscope 

 slight irregularities exist where the faint lines of growth intersect 

 the sulci. The shells are slightly more tumid than that repre- 

 sented by the figure given by Professor Tate; the other specific 

 characters, however, are identical in the main, and the present 

 writer hesitates to make a specific distinction on such unimportant 

 diiferences. The species is evidently very variable; even the 

 deep sulcation bordering the suture (so prominent in the speci- 

 mens selected for description by the last- mentioned author) is 

 occasionally reduced to such dimensions that it barely surpasses 

 in size the ordinary spiral sulcations. The latter, too, are by no 

 means always persistent over the whole of the whorls, one of the 

 Museum specimens showing the body-whorl sulcated over two- 

 thirds of the surface only. It would seem that when ornamented 

 in the manner lastly described, the sulcation bordering the suture 

 is stronger, as though the missing sulci had gathered together 

 at that point. On the other hand, when sulcated throughout, the 

 sutural sulcus is relatively smaller — a phenomenon observable also 

 in certain European forms of Act^onid^, where it seems to be 

 merely an individual characteristic. Q'he visible portion of the 

 protoconch (Plate I. Figs. 2a-l) consists of about H turns, and 

 is remarkably small, hiding the sinistral nucleus — at least in the 

 Museum specimens. 



Dimensions. — Length 5-5 mm. ; breadth 3 mm. ; length of 

 aperture 3 mm. 



Form, and Loc. — Eocene : Adelaide. 



G. 9305. Three specimens. Purchased. 



Genus ADELACT..ffiON, Cossmann. 



[Ess. Paleoconcli. Comp. 1" liv. 1895, p. 54.] 



Mijonia, A. Adams, Ann. Mag. Nat. Hist. 3rd ser. vol. v. 1860, 

 p. 406 {non Dana, 1847). 



Protoconch with sinistral nucleus ; not very large. Sutures of 

 the shell canaliculated, or impressed ; whorls decussated by fine 



