398 SHELLS. 



trigono-orbiculari, convexo-compressa, prsecipue ad umbones, 

 umbonibus submucronatis, lateribus concavo-declivibus, areis 

 subauguste excavatis, valvis circa umbones confertim sulcatis, 

 deinde Isevibus ; calcareo-alba, epidermide intense nigro-cas- 

 tanea induta. 



This fine species, of which specimens were first collected by 

 Sir John Richardson at the mouth of the Mackenzie River, 

 may be at once distinguished from those next allied to it, A. 

 lactea and Islandica, by its more compressed growth and the 

 attenuated prominence of the umboes, from which the nar- 

 rowly excavated areas on each side slant almost concavely. 



A. fabula (PI. XXXIII. Fig. 5 a, b) . Ast. testa transverse 

 ovata, cornpressa, versus umbones subtrigona, lateribus utrinque 

 subconcavis, deinde rotundatis, circa umbones regulariter sul- 

 cata, deiude Isevigata aut striis incrementi notata, areis late- 

 raUbus parum excavatis ; fulvescente-castanea. 



Of a compressed triangularly -ovate form, more than usually 

 transverse. 



A. globosa (PL XXXIII. Fig. 6 a, b}. Ast. testa subtri- 

 gona, ventricosa, transversim minute sulcata, luteo-fusca, parte 

 anteriore promiuente rotundata, parte posteriore obtusa, trun- 

 cata. Moller, Moll. Index Groenlandise, p. 20. 



Distinguished particularly from all other species of the genus 

 by its globose, heart-shaped, Cyclas-like growth. 



CARDIUM (Linuaius). 



C. Grcenlandicum, Chemnitz, Conch. Cab. vol. vi. pi. 19. 

 f. 198. 



C. edentulum, Sowerby. 

 Aphrodite columba, Lea. 

 C. ciliatum, Fabricius. 

 C. Fabricii, Deshayes. 



TELLINA (Linnjeus). 



T. proxima, Brown, Zool. Beechey's Voy. p. 154. pi. 44. 

 f. 4. 



