75 



Genus 17. CONCHOLEPAS, Lamarck. 



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

 head fattened, prolonged on each side into two tentacles, the 

 loiver portion of which is thickened and truncated ; eyes situated 

 at the summit of the truncated portion; proboscis obtuse; 

 respiratory siphon rather small. 



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

 and imbricated ; aperture very large and inflated, Up furnished 

 at the base with two or three projecting 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 was of a spiral or non- 

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

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

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

 appearance of a compressed cornucopia, with the margin of the aperture 

 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, 

 according to the method originally adopted by Lamarck. 



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



Figure. 



Concholepas Peuuvianus. 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 flatfish, 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 Unieomus, is characterized solely by the 



l2 



