52 , NUCULID.K. 



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

 latam prominens. Margo dorsalis uterque declivis et rectus : 

 ventralis regulariter arcuatus, haud sinuatus, intus crenatus ; 

 cardinalis latus. Dentes pauci : fossa cartilagiiiis perparva, haud 

 obhqua. — Minute, trianguhir, uot elongated, rather oblique, ven- 

 tricose at the umboes, elsewliere 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 and numerous radiating lyrse. Hinder side not so short 

 as usual, subangular and prominent at its extremity. Ventral 

 margin regularly arcuated, not sinuated, coarsely crenated within. 

 Beaks pecuharly 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 cremdated. 



22. N. Pdelcha, LfOrh., 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, haud sinuatus. Nates 

 eminentes, acutse. Lunula angulatim 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. 

 Pront dorsal region undefined. Cartilage not horizontal. Teeth 

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

 of n'ltida and convexa, are iu 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, vaUda, obUque 

 ovata, vix ventricosa, subleevigata, valde insequiiaterahs, radiis haud 

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

 angulata. Margo dorsalis anticus convexus satisque dechvis; 

 posticus declivis, subrectus vel subretusus; ventralis arcuatus, 



