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Genus 17. CONCHOLEPAS, Lamarch. 



Animal ; disc oval, large, famished posteriorly with an operculum ; 

 head flattened, prolonged on each side into tivo tentacles, the 

 lower portion of which is thickened and truncated ; eyes situated 

 at the summit of the truncated piortion ; proboscis obtuse ; 

 respiratory siphon rather small. 



Shell ; ovate, spire very short, minute, apex sharp ; tohorls ribbed 

 and imbricated ; aperture very large and inflated, lip furnished 

 at the base with two or three 23TOJecting teeth. 



The term Concho-Lepas, applied to this shell in a generic sense by 

 Lamarck, seems to have emanated from the difficulty which our concho- 

 logical ancestors found in determining whether it w^as of a spiral or non- 

 spiral structure ; shells of the former growth, being designated by the title 

 of Cochlea or Conchs, of the latter, meaning the Limpets, by that of Lepas 

 or rock shells. The spire is extremely minute, and the sheU has all the 

 appearance of a compressed cornucopia, with the margin of the apertui'e 

 reflected outwards like the mouth of a trumpet. 



The animal appears to differ in no respect from that of Purpura, and our 

 continental neighbours are unwilling that it should occupy any higher rank 

 than as a section of that genus ; the characteristic variation in the growth 

 of the shell is sufficient, however, to warrant its separate arrangement, 

 accorcUng to the method originally adopted by Lamarck. 



The genus is only represented by the following species, found at Peru. 



Figure. 



CoNCHOLEPAS Peruvianus. Plate 5. Pig. 27. Shell, showing its widely 

 inflated, Limpet-like, aperture. 



Genus 18. MONOCEROS, Lamarck. ^ 



Animal ; similar to that of Purpura. 



Shell ; ovate, spire sometimes elevated, sometimes rather depressed, 

 columella wide and flattish, sometimes indistinctly plaited, lip 

 armed near the base with a sharp prominent recurved tooth. 

 Operculum horny. 



The genus Monoceros of Lamarck, introduced almost simultaneously by 

 De Montford under the title of Unicornus, is characterized solely by the 



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