156 NUCULID.E. 



posticum (pro genere ejus) liaud breve, ad extremitatem subangu- 

 latam prominens. Margo dorsalis uterque declivis et rectus : 

 ventralis regulariter arcuatus, baud sinuatus, intus crenatus; 

 cardinalis latus. Dentes pauci : fossa cartilaginis perparva, baud 

 obliqua. — Minute, triangular, not elongated, rather oblique, ven- 

 tricose at the umboes, elsewhere more or less compressed, rectan- 

 gular above (the dorsal slopes being straight and decided) , glossy, 

 everywhere concentrically costellated ; the interstitial sulci, except 

 perhaps on the undefined and inconspicuous dorsal areas, adorned 

 with fine arfd numerous radiating lyrrc. Hinder side not so short 

 as usual, subangular and prominent at its extremity. Ventral 

 margin regularly arcuated, not sinuated, coarsely crenated within. 

 Beaks peculiarly high, and laterally compressed. Hinge-margin 

 broad : teeth few (ten and six) ; pit minute, perpendicular. — Pos- 

 sibly immature, but strongly characterized. The specimens were 

 dead and devoid of epidermis. 



Sect. B. Margins not crenulated. 



22. N. Puelcha, I/Orb., f. 149. — T. ovato-trigona, subven- 

 tricosa, inferne tantum rude corrugata. Extremitas antica inferne 

 rotundato-subangulata ; postica inferne acute obtusangularis ; 

 margo posticus rectiusculus satisque obliquus. Margo ventralis 

 arcuatus, integer, postice multum acclivis, baud sinuatus. Nates 

 eminentes, acutse. Lunula angulation circumscripta, impressa, 

 satis magna, vix protrusa. Area haud definita. Dentes multi. 

 Cartilago haud horizontalis. — Ovate-triangular, not particularly 

 oblique, subventricose, coarsely wrinkled concentrically near the 

 ventral margin. Front extremity subangulately rounded below. 

 Hinder side not so very short for the genus, sharply obtusangular 

 below ; the posterior edge not perpendicular, straightish. Ventral 

 margin arcuated, entire, much and somewhat more straightly 

 rising behind, without posterior refusion. Beaks elevated, acute. 

 Lunule rather large, impressed, angularly defined, scarcely pouting. 

 Front dorsal region undefined. Cartilage not horizontal. Teeth 

 numerous. — D'Orbigny's types of this species, which remind us 

 of nitida and convexa, are in sorry condition, without epidermis, 

 and worn smooth. There seem some close lamellar wrinkles upon 

 the lunule, but of this I am not sure. 



23. N. obliqua, Lam., f. 150. — T. magna, valida, oblique 

 ovata, vix ventricosa, subkevigata, valde insequilateralis, radiis haud 

 picta, intus argentea, antice rotundata, postice inferne rotundato- 

 angulata. Margo dorsalis anticus convexus satisque deckvis; 

 posticus declivis, subrectus vel subretusus; ventralis arcuatus, 



