150 



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

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



Species. 



1. brunnea (Eul.), Sow. 2. imbricata, Sow. 3. interrupta (Eul.), Sow. 



4. marmorata, Soto. 5. splendidula (Eul.), Sow. 



Figure. 



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

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



Genus 20. RISSOA, Freminville. 



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

 pointed behind, 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, Up generally thickened and more or less produced. 



The species composing this genus being for the most part extremely 

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

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

 when M. Freminville paid him the compliment of associating them under a 

 new generic type with his 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 will be greatly increased, as the same powers 

 of observation become extended to more distant localities. 



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

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

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



