7;o 



DIVISIONS OF THE GASTROPODA. 



Fig. 657. — Haliotis tuber- 

 culata, from the Pliocene 

 Tertiary. 



Family 7. Haliotid^. — In this family the shell (fig. 657) is 

 spiral and ear -shaped, nacreous internally, and with a large aper- 

 ture. The body-whorl exhibits on the left side a series of rounded 

 perforations, which become successively filled 

 up, the last few, however, remaining always 

 open. The last of these apertures corre- 

 sponds with the anus and transmits a fold 

 of the mantle, while the others give passage 

 to tentaculiform prolongations of the pallial 

 border. This family contains only the genus 

 Haliotis, comprising the recent "Ear-shells." 

 The oldest example of this genus is the H. 

 antiqua of the Maestricht Chalk, and a few 

 Tertiary species are known. 



Family 8. Stomatiid^e. — In this family 

 the shell is spiral or ear-shaped, with a short 

 spire, and an expanded entire aperture. The 

 interior is nacreous, and the shell is destitute 

 of the perforations which characterise Halio- 

 tis. The principal genus in this family is Stomatia, the earliest 

 undoubted representatives of which appear in the Jurassic rocks, 

 while others are Cretaceous and Tertiary, and a few forms still 

 survive. 



Family 9. Euomphalid^:. — As defined by De Koninck, the 

 genera comprised in this family possess a spiral shell, sometimes 

 elevated, sometimes discoid, the whorls being in contact or disjunct, 

 and a larger or smaller umbilicus being present. The outer lip of the 

 aperture exhibits one or two (rarely three) larger or smaller sinuses, 

 of which the surface often shows only slight traces, except that their 

 existence is usually marked by keels or by imbricated lamellae of 

 growth. The inner portion of the shell is often partitioned off by 

 successively produced transverse septa ; and a shelly operculum is 

 sometimes present. Professor De Koninck includes in this family 

 a number of extinct, mostly Palaeozoic, genera, which are probably 

 in some cases referable to different groups, but which will be here 

 considered together, as a matter of convenience. On the other 

 hand, none of the genera placed here by De Koninck are admitted 

 into this family by Lindstrom except Euomphalus proper, while by 

 this authority Loxonema is associated with Euomphalus. 



The two principal types included in the Euomphalida, as defined 

 by De Koninck, are Straparollus and Euomphalus, which many 

 authorities have regarded as so nearly related as to have merely the 

 standing of sub-genera, while Lindstrom considers them as belong- 

 ing to entirely different families. In Straparollus (fig. 658) the 

 shell is thick, typically conical, with a more or less prominent spire 



