1890.] MARINE MOLLUSCA OF ST. HELKNA. 313 



II. PELECYPODA. 



Saxicava arctica (Linn.). 

 Hab. Cosmopolitan. 



Kellia crassitjscula. (Plate XXIV. fig. 23.) 



Testa f/lohosa, rotimde ovata, nitida, alba, apices versus suhpellucida, 

 concentrice subrugose striata, fere cequilateralis ; latus anticum 

 posteriore paulo anrfustius ; pa(/i>trt interna alba, incrassata, 

 minute subrwjosa ; linea cardinalis crassiusoula, dente veltuber- 

 culo cardinali et laterali iwsteriore tuberculari in utraque valva 

 instructa ; ligamentum internum pone umbones situm. 

 Longit. Q\ mlllim., alt. 5, diani. 3|. 



For a shell of such small size it is rather thick. The umbones 

 are only very slightly elevated, curved towards the anterior end, and 

 capped at the tip with a minute embryonic shell. 



Kellia atlantica. (Plate XXIV. fig. 24.) 



Testa minuta, ohlongo-rotundata, incequilateralis, sordide alhida, 

 concentrice tenuissime striata ; margo dorsi anticus vcdde declivis, 

 leviter convexus, posticus longior, subhorizontalis ; latus anticum 

 acute rotundatum, posticum latins excurvatum ; margo inferior 

 late arcuatus. Dens cardinalis valvce sinistrce ^-foi'mce, vcdvce 

 dextrce unicus prominois, acutus ; dens lateralis posticus in 

 utraque valva elongatus, in dextra validus, margine dorscdi sulco 

 separatus. 



Longit. 2^ millim., alt. 2, diam. Ig. 



This species is about the size of Lepton clarJcics, but not of the 

 same form. 



MoNTAcuTA subtriangularis- (Plate XXIV. fig. 25.) 



Testa fere cequilateralis, mediocriter convexa, sordide alhida, haud 

 nitida, rotunde suhtriangularis, lineis incrementi striata, postice 

 qtiam antice paulo angustior ; margo dorsalis utrinque declivis, 

 postice vix excurvatus, antice leviter concavus, ventralis rectus vel 

 in medio leuissime incurvatus ; umbones p>rominuU, subacuti ; 

 pagina interna nitida, prope margine incrassata ; cicatrices 

 magnce, subpyriformes ; dentes duo valvce sinistrce prominentes, 

 divergentes. 



Lonr/it. 4| millim., alt. 3g, diam. 2g. 



This species has the dorsal margin sloping on each side and the 

 base almost straight, so that a somewhat triangular shape is produced, 

 the two lower angles being well rounded. 



LuciNA (Codakia) imbricatula, C. B. Adams. 



Lucina imbricatula, C. B. Adams, Proc. Boston Soc. Nat. Ilist. 

 1845, vol. ii. p. 10 ; id. Contrib. Conch, p. 245. 



