1890.] MARINE MOLLUSCA OF ST. HELENA. 285 



Lacuna pumilio. (Plate XXIII. fig. 31.) 



Testa minuta, albida, late umbilicata, subglobosa, incrementi lineis 

 obliquis striata, aliis spiralibus obsoletis subeaiicellata ; an- 

 fractus tres, convexi, ultimus supra tabulatus et subanyulatus, 

 uiferne carinis duabus cinctus ; upertura irregulariter ovata, 

 magna, lonc/it. totius ^ adcequans ; columella fere rectilinearis, 

 anguste reflexa, inferne producta, carince umbilicum circumdanti 

 juncta, 

 Longit. \k millim., diam. \h. 



Although so small, this does not look like a young shell. Of the 

 two keels on the base of the body-whorl, that bordering the umbilicus 

 is the more conspicuous, and unites with the lower extremity of the 

 columella ; the other runs into the base of the aperture, a little 

 farther off", and the space between is somewhat flat. 



Fossarus ambiguus (Linne'). 



Hah. Many parts of the Mediterranean, the coast of Morocco, 

 Cape A'^erde Islands and Senegal, Madeira and the Canary Islands. 



The specimens from St. Helena, which I believe belong to this 

 species, present a very great variation iu form. Some closely 

 resemble Adanson's figure (Seue'gal, pi. 13. fig. 1), but are rather 

 more widely umbilicated. The majority, however, have the spire 

 scarcely elevated above the body-whorl, the mouth large, and the 

 umbilicus very open, so that, in many cases, the hody-whorl is 

 detached from the preceding for a short distance. 



The spiral keels, also, are very variable in number and thickness, 

 but all specimens exhibit very much the same kind of fine spiral 

 strise upon and between the ridges. I see no reason for separating 

 F. cumingii of A. Adams from this species ; and F. bicarinatus of 

 the same author may also be an extreme form of it. 



FossARXJS (Couthouyia) dentifer. (Plate XXIII. fig. 32.) 

 Testa parva, alba, minute rimata, solida, hand nitens ; an/ractus 

 5-6, apicalis globosus, invulutus, cceteri conoexi, superne obsolete 

 angulati, lineis incrementi rugosis obliquis striati ; anfr. ulti- 

 mus magnus, globosus, liris spiralibus distantibus paucis {circiter 

 sex) cinctus ; apertura subcircularis, longit. totius | adcequaiis ; 

 labrum tenue, superne hand sinuatum ; columella arcuata, 

 callosa, infra medium transverse plicata, infra plicam late 

 excavata. 

 Longit. 2 millim., diam. max. 1|. 



The general character of this shell seems to refer it to this genus, 

 but it diifers from other species in having a columellar denticle. 



The genus Plicifer of H. Adams (Proc. Zuol. Soc. 1868, p. 293) 

 was founded for a small white shell with a somewhat similar tooth 

 or fold on the pillar. P. nevilli, however, has a posterior sinus to 

 the labrum, and differs in other respects from the present species. 



Fossarus (Couthouyia) l^eviusculus. (Plate XXIII. fig. 33.) 

 Testa parva, anguste umbilicata, ovata, superne acuminata, alba, 

 Proc. Zool. Soc— 1890, No. XX. 20 



