G9 



Genus 12. LEPTOCONCHUS, Bwppell. 



Animal; proboscis elongated, retractile; tentacles two, smooth, 



triangular, jointed internally at the base, and bearing the eyes 



externally i?i the middle ; disc middling, no operculum ; mantle 



circular at the edge, without any siphonal appendage, a little 



produced on the left side ; branchial orifice rather large. 



Shell ; thin, pellucid, nearly globose, spire depressed, rather ob- 

 solete ; aperture large, suboval, extremities turned contrariwise, 

 margins disjointed, right margin thin, a little expanded ante- 

 riorly ; umbilicus none, truncated anteriorly, contorted. 



Such are the descriptions of Leptoconchus recorded by Dr. Riippell, in his 

 communication to the Zoological Society of London in September, 1834- 

 It is allied to the Magilus, with this difference, the margins of the aperture 

 are not united, and by reason of its dwelling in exposed cavities of madre- 

 pore, forms no extended tubular growth. 



"The colour of the shell," says the learned traveller, "which constitutes 

 the type of this new genus, is constantly a slightly sordid milk-white. It 

 is sulcated externally by numerous longitudinal undulated closely-set lines, 

 the outer whorls encroaching on the spire of the earlier ones so as almost 

 to obliterate it. Individuals of all ages have the shell thin and fragile, and 

 constantly occur imbedded in the calcareous mass of polypes, having a com- 

 munication with the sea by only a moderate opening. The animals of 

 Magilus and Leptoconchus are distinguished by the presence and absence of 

 an operculum, and by the difference in the proboscis ; the siphon of the 

 former, moreover, does not occur in the latter."* 



Dr. Riippell suggests that Leptoconchus might be arranged in the vicinity 

 of Tanthina, I cannot, however, subscribe to tins opinion, the habits and 

 structure of these mollusks being so totally dissimilar. 



Figure. 



Leptoconchus striatus. PI. 4. Fig. 20. Showing, a and b, back and 

 front view of the shell ; c, as it appears imbedded in a mass of coral. — 

 From Mr. Cuming's collection. 



Pro Zool. Soc. 1834. p. 105. 



