182 EOCENE MOLLUSCA. 



In the general form of the shell, the condition of the apex and of the outer lip, 

 the columellar plaits, and the deep anterior notch, this Mitra so much resembles 

 M . lubratula, that it might almost be regarded as merely a variety of that species in 

 which the longitudinal ribs and transverse lines found in the young state have been 

 continued on the mature shell. I have not, however, met with any smooth specimen 

 of the present species, and mature individuals of M. labratula are, apparently, always 

 smooth, with the exception of a few obscure transverse lines near the suture, or at the 

 base. This want of intermediate forms, therefore, confirms the title of M. scabra to 

 specific distinction. 



Size. — Axis, ll-12ths of an inch; diameter, 5-12ths of an inch. 



Locality. — The species appears to be confined to the Barton beds. I have not 

 met with it elsewhere. 



No. 119. Mitra labratula. Lamarck. Tab. XXIV, fig. 3 a, b. 



Mitra labratula, Lamh. 1803. Ann. du Mus., vol. ii, p. 58, No. 5, t. 3, fig. 6. 



— labratella, lb. 1816. Tab. Encycl. et Method., t. 392, fig. 3 a, b. 



— labratula, lb. 1822. Hist. Nat., vol. vii, p. 325, No. 5. 



— — Defr. 1824. Diet, des Sci. Nat., vol. xxxi, p. 491. 



— — Desk. 1830. Encyc. Method, (vers.), vol. ii, p. 465, No. 42. 



— — lb. 1824—37. Descr. des Coq. Foss. &c, vol. ii, p. 672, t. 88, figs. 



9, 10, 18 and 19. 



— — Mellev. 1843. Mem. sur les Sables tert. inf., &c, de Paris, p. 17. 

 — — Roissy. . Buff. Moll., vol. v, p. 443. 



— monodonta, Sow. (non Lamk.) 1850. Dix. Geol., &c, Suss., p. 106, t. 7, figs. 20, 21. 



— labratula, If Orb. 1850. Prod, de Paleont., vol. ii, p. 354, No. 296. 



M. testa ovato-acutd, lavi, aliquando injiwentd costulis et striis transversis decussatd, 

 ad basin profunde emarginatd .- spird conicd, apice obtuso : aperturd elongatd, angustd ; 

 labro incrassato, sub-marginato, intus unidentato ; columella quadriplicatd. 



Shell ovately oblong, slightly ventricose, smooth; sometimes in French specimens 

 the early volutions present obscure undulating ribs, decussated by irregular, transverse, 

 fine, raised lines, which altogether disappear on the last volution, or are reduced to a 

 faint lines, nearly obsolete, at the base, or round the sutural margin : the spire is 

 conical with an apex formed, like that of M. scabra, of two roundish embryonal whorls, 

 and. as in that species, the base is deeply notched, and bent backwards. The aperture 

 is of a long, ovate shape, and rather narrow ; the outer lip thickened, slightly bent 

 outwards, so as to form a narrow, raised border along the outer margin, and furnished, 

 generally, with a blunt, tooth-like callus on the inner edge, near the posterior extremity ; 

 the columella presents four prominent, almost transverse folds, the posterior three of 

 which are nearly equal, and are larger than the one in front. 



