ADELACTiEON. 11 



stria3, lines of growth inconspicuous; columella slightly excavated 

 and carrying a small but well-marked plication ; columellar border 

 expanded and frequently covering the small umbilicus. 



This genus resembles Actaon in its general characters, but may 

 be readily distinguished when the earlier portion of the protoconch 

 can be satisfactorily determined ; the protoconch, as a whole, is 

 not so well developed as in Adceon. 



In proposing this new name for Myonia, M. Cossmann remarks 

 that the fossil forms slightly differ from the living, and he bases 

 a new description and diagnosis on a Miocene species, Acteeon 

 papyraceus, Basterot, from the neighbourhood of Bordeaux, quoting 

 that species as the type of the genus. But, in substituting a 

 generic name for one preoccupied, it is desirable to conform to 

 usage by quoting as the type of the genus that appertaining to the 

 genus displaced ; therefore the type species proposed by the French 

 author alluded to should be superseded by that referring to Myonia. 



Type. — Myonia japonica, A. Adams. 



Adelactaeon olivellaeformis, Tate (sp.). 



1894. ActcBopyramis oUvellaformis, Tate, Journ. Roy. Soc. N.S.W. 



vol. xxvii. p. 181, pi. xi. fig. 2. 



1895. Adelactieon oUvellaformis, Cossmann, Annuaire Geol. Univ. t. x. 



p. 756. 



Protoconch (Plate I. Figs. 3a-b) small, earlier portion hidden 

 by later turns in many specimens, but comparatively free in the 

 one now figured. It is smooth and polished ; more elevated than 

 in A. papyraceus, and is implanted obliquely on succeeding whorls. 

 Shell as a whole elongate ; aperture less than half the total length 

 of the shell ; whorls slightly turriculate, smooth, with minute 

 spiral strias, which become more prominent on the anterior portion 

 of the body-whorl. 



The classification of this species, as remarked by M. Cossmann 

 {op. cit. supra), is a matter of doubt ; the embracing character of 

 the last whorl is distinctly that of the Act^onid^, but the earlier 

 part of the protoconch is different to that of Adelactaon, which, 

 sensu stricto, is obtuse, and is implanted in such a manner as 

 to render its sinistral character hardly perceptible. 



