1890.] MARINE MOLLUSCA OF ST. HELENA. 289 



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



Testa ovata, umlilicnta, albo-jjellucida, nitida ; anfractiis 4, 

 sutura profunda dlscreti, convexl, duo supremi Icevis, cceteri 

 striis spiralihus tenuissimis sculpti, ultlmus inagniis, sub- 

 glohosus ; umbilicus falcifonnis, in medio lira fenuissima 

 instructus ; apertura rotunde ovata, superne acuminata, 

 longit. totius g cequans ; peristoma continuum, vix incras- 

 satum, ad basim columellas subeffusum vel indistincte sub~ 

 canaliculatum. 

 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 columella, and also differs in other particulars. 



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



Testa ovata, imperforata, nitida, subpellucida, lineis spiralihus 

 fuscis interruptis ornata ; anfractiis 5, convexi, duo supremi 

 minuiissime subpunctati, cceteri spiraliter sulcati, sutura 

 profunda sejuncti ; apertura ovata, superneleviter acuminata, 

 longit. totius h liaud cequans; peristoma tenue, margine 

 columellari anc/uste reflexo, superne labro callo tenui juncto. 

 Longit. 1| 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 5, convexi, sutura profunda discreti, sulcis 

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

 12) sculpti ; apertura rotunde ovata, superne Icviter acuminata., 

 longit. totius \ liaud cequans ; peristoma eontinuum, vix in- 

 crassatum, ad basim obsolete expansum. 

 Longit. 2 millim., diam. 1. 



AVhen 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-Q, primi duo spjiraliter tenuiter striati, cceteri plani- 

 usculi, carinis voJventihus prominentibus {in anfr. superiorihus 

 trihus, in ultimo 7-8) instnicti , sutura profunda sejuncti; apertura 

 ovata, longit. tofms ^ luiulo superans ; peristoma continuum, 

 margine externa leviter incrassato, cohnneJlari antice subdilaiato. 



Longit. 'S millim., diam. 1^. 



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



