NAVICELLA. 



Lmn, Hist. Nat. des Anim. sans vert. VI. pt.2. p. 181. 



TESTA transversim elliptica, vel oblonga; su- 

 pernfe convexa, subtus concava ; spira nulla ; 

 vertice ad marginem suboblique inflexo. Labium 

 internum complanatum, acutum, angustum, 

 edentulum; externum acutum, integrum. Im- 

 pressiones musculares duae, distinctae, eloiigatae. 

 Operculum testaceum, subquadratum, planum, 

 dente lateral!, acuto, instructum. 



n 



Ll\marck has placed this Genus in a situation which it 

 appears very naturally to occupy, close to his Neritina, to 

 which it indeed seems to bear the same degree of affinity 

 that Ancylus of Miiller does to Limnea. In attempting to 

 draw up a generic character for this shell, it will be ob- 

 served, that we have followed Lamarck very closely, 

 though we are not quite convinced of the propriety of 

 doing so, because, on account of its near affinity to spiral 

 shells, we should gladly have used the terms commonly 

 applied to such, instead of those more commonly used in 

 describing patelliform univalves. The general form of the 

 shells which compose this Genus is, however, so similar to 

 many Patellae, and the definition, moreover, will be so 

 much more easily understood, that we think we are war- 

 ranted in continuing Lamarck's application of these terms. 

 We are not aware that there will be any difficulty in dis- 

 tinguishing this Genus from all others ; the absence of 

 spiral volutions and the large aperture will separate it 

 froni Neritina, while its shelly operculum and the regu- 

 larity of its form will serve as discriminating characters 



