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Genus 1. NAVICELLA, Lamarck. 



Animal ; ovately oblong, rather slight, the disk occupying the wide 

 aperture of the shell, with a peculiar quadrangular slightly 

 radiated operculum, insinuated between it and the visceral 

 mass ; head flattened and auriculated, with two large subulate 

 tentacles, at the outer base of which are two other short trun- 

 cated tentacles, bearing the eyes. 



Shell ; transversely elliptic or oblong, Limpet-shaped, spire very 

 short, columella depressly flattened, forming a transverse shelf 

 last whorl extremely patent, and marked with two muscidar 

 impressions. 



A small genus of fresh-water mollusks, whose shells are remarkably 

 depressly convoluted, and very similar in appearance to those of the Crepi- 

 dulce or Slipper-Limpet, the columella being transformed into a flattened 

 septum, forming a shelf, as it were, across one side of the aperture. The 

 NavicettcB are, however, very distinct from the Crepidula, and have little 

 affinity with any of the Limpet tribe ; they are not of the same parasitical 

 habits, and live free in flowing streams. Their shells are of regular symme- 

 trical formation, and not subject to the distorted irregularities of growth 

 which is the common lot of those living attached to the rough-hewn 

 surface of the rocks. 



The painting of the Navicetta shells is generally of a mottled character, 

 in lines or sab triangular patches radiating from the apex, covered with a 

 thin fibrous olive epidermis, and the interior is mostly of a bluish tinge. 

 The operculum is composed of two parts, one of which is internal, imbedded 

 between the middle of the disk and the viscera, occupying the spiral 

 chamber of the shell, the other is of stouter substance and appears to radiate 

 at a right angle with the former. 



The Navicetta are unknown to Europe and the western Hemisphere ; 

 they inhabit the streams of the Philippine and Feejee Islands, and are 

 found in New Guinea, New Ireland, New Holland, and in Mauritius and 

 the neighbouring Isles, where they are said to be eaten by the poorer 

 natives for food. The largest species, selected for illustration, is prettily 

 variegated with yellow upon a dark olive-black ground ; for delicacy of 

 form and colouring the N. lineata and Recluzii are perhaps the most 

 interesting species. These two last mentioned are of a compressly oblong 

 form, resembling a fragile boat, of which the septum forms the poop. 



