1890.] MARINE MOLLUSCA OF ST. HELENA. 289 



RissoA ERiTiMA. (Plate XXIII. fig. 40.) 



Testa ovata, umlilicata, alho-2')eUucida, intida ; anfraclus 4, 

 sutura profunda discreti, convexi, duo supremi leevis, cceteri 

 striis spiralihus teniiissimis sculpti, uUimus majnus, sub- 

 glohosiis ; umhillcus falciformis, in medio lira fenuissima 

 instructus ; apertura rotunde ovata, superne acuminata, 

 longit. totius h, cequans ; peristoma contimmm, vix incras- 

 satum, ad hasim columellce subeffusum vel indistincte sub- 

 canalicnlatum. 



Longit. 1§ millim., diam. 1. 



This is more widely umbilicated than R. soluta, Philippi, is more 

 regularly spirally striated, has a slight indication of a sinus at the 

 base of the cohmiella, and also differs in other particulars. 



RissoA AGAPETA. (Plate XXI. fig. 23.) 



Testa ovata, imperforata, nitida, suhpeUucida, lineis spiralihus 

 fuscis interrnptis ornata ; anfractus 5, convexi, duo supremi 

 mimitissime suhpunctati, cceteri spiralifer sulcati, sutura 

 profunda sejuncti ; apertura ovata, superne leviter acuminata, 

 lonqit. totius h Jiaud aqtians ; peristoma tenue, margine 

 columellari amjuste reflexo, superne labro callo tenui juncto. 

 Longit. If millim., diam. fere 1. 



The microscopic sculpture of the apical whorls has a very pretty 

 shagreened appearance. The spiral sulci are about five in number 

 on the penultimate volution, and twelve on the last. The uninter- 

 rupted brown lines fall on the ridges between the grooves. R. de- 

 picta, Manzoni, from Madeira, is an allied but larger form. 



RissoA COMPSA. (Plate XXIII. fig. 41.) 



Testa ovata, inperforata, parum nitida, albida vel dilute fus- 

 cescens ; anfractus^i, convexi, sutura profunda discreti, sulcis 

 spiralibus fortihus {in anfr. penult, circiter 5, in ultimo ad 

 12) sculpti ; apertura rotunde ovata, siiperne leviter acuminata, 

 longit. totius J- Tiaud cequans ; peristoma continuum, vix in- 

 crassatuni, ad hasim obsolete expccnsum. 

 Longit. 2 millim., diam. 1. 



When placed side by side, this species is seen to be a trifle larger 

 than R. agapeta, and a little smaller than R. depicta. It also 

 differs from both in colour, and is more strongly grooved than 

 either. 



RissoA WALLiCHi. (Plate XXI. fig. 24.) 



Testa ovata, solida, alba, interdum zona rufa cincta, imperforata ; 

 anfractus 5-6, primi duo sp/iraliter tenuiter slriatl, cceteri plani- 

 uscidi, carinis volve.ntihus prominentihus {in anfr. superiorihus 

 trihts, in ultimo 7-8) instructi,sxitur a profunda sejuncti; apertura 

 ovata, longit. totius g paulo superans ; peristoma continuum, 

 margine externa leviter incrassato, columellari antice subdilatato. 



Longit. 3 millim., diam. 1|. 



The red zone, when present, occupies the central part of the last 



