150 



obtained at St. Elena, West Columbia, and the N. interrupta was dredged 

 in the Gulf of Nicoiya. The N. hrunnea is reported to be from China. 



Species. 



1. bruunea (-E^e<^.)> Sow. 2. imbricata, Sow. 3. interrupta {Eul.), Sow. 



4. marmorata. Sow. 5. splendidula {Eul.)^ Sow. 



Figure. 



Niso SPLENDIDULA. PI. 15. Pig. 79. Shell, showing its sinuated aperture 

 and very deep umbihcus. — From Mr. Cuming's collection. 



Genus 20. RISSOA, Freminville. 



Animal ; disk elongated, soynewliat triangular, truncated in front, 

 pointed heliind, and furnished with a horny operculum ; head 

 cylindrical and proboscis-shaped, having a long pointed ten- 

 tacle on each side, at the outer base of which are situated the 

 eyes. 



Shell; turriculated, enlarged at the base, rarely umbilicated ; 

 sometimes short ; aperture oval, semilunar, slightly chan- 

 nelled, lip generally thickened and more or less produced. 



The species composing tliis genus being for the most part extremely 

 small, they have been much neglected by conchologists. M. Eisso appears 

 to have been the first to observe their claim to rank as a particular genus, 

 when M. Preminville paid him the compKment of associating them under a 

 new generic type with liis name. Lamarck included the few species known 

 to him under the head of Melania, but various species have been described 

 since that period by MM. Desmarest, Michaud, and Philippi, including the 

 animal as above described. 



Several of these inhabit the Mediterranean, between twenty and thirty 

 have been now observed on the shores of the British Isles, and it is not 

 impossible that the number wiU be greatly increased, as the same powers 

 of observation become extended to more distant locahties. 



The shell may be chiefly recognised from its being enlarged at the base, 

 whUst the upper part of the aperture is slightly channelled ; the lip is 

 mostly thickened and more or less produced or expanded. The following 



