NUCUl.ID.E. 6 



nearly so, ohversulv subcuneiforin, almost siinilar, but the front one 

 is slightly Uic broader and more rounded, the hinder slightly the 

 more tapering, and subbiangulated at its extremity. Dorsal edge 

 horizontal, very slightly liexuous (pi mo-convex in front, plano- 

 retuse behind). Ventral margin subarcuated, the arch usually a 

 little straightened or even subretuse in (he middle, convexly rising 

 at both ends, yet with a slight retusioii in front, and in a straight- 

 ened line behind. Beaks not at all elevated. Dorsal areas in- 

 conspicuous, the hinder one flattened. Teeth most numerous on 

 both sides ; pit shallow, broadly triangular, sunken. 



3. L. SowEiiBiANA, B'Orh., f. 33. — T. L. elongate simillima, 

 sed nivea, angustior, utrinque acutior, et fere usque ad extremi- 

 tatem posticam scalpta striis arctioribns, quarum antiee et con- 

 centricse sunt etiamque oblique longitudinales. Areas dorsales trans- 

 yersira costulatiE. — Iridescent, snow-white, most closely resem- 

 bling elongata, yet rather narrower, and with more taper extremi- 

 ties. The strise, also, which are still finer and closer, and just in 

 front are both concentric and obliquely longitudinal, extend as far 

 as the ordinary site of an umbonal ridge. Dorsal areas more or 

 less distinctly cross-barred. In adult examples the fine central 

 stria; (at least in one of the valves) seem raised, and the lines of 

 growth cut the somewhat slanting longitudinal ones before the 

 smooth site of an umbonal ridge. In the young the escutcheon 

 is excavated, and its edges crenulated : the hinder extremity of 

 the valves, moreover (as may be seen in the nuclear portion of the 

 full-grown shell), is, also, subobli([uely striolate. D'Orbigny, 

 aware that the South American laticeolata of Sowerby was not 

 identical with the Lamarckian one (a species without adequate 

 definition, either verbal or pictorial), termed it (Voy. Amer. 

 Merid. Moll., p. 5 14) SoiccrL//ana, but with his usual carelessness 

 referred to the figure in the 'Genera' {electa), instead of that in 

 the ' Illustrations.' 



3. L. Patagonica, D'Orbigtu/, f. 49, -^0.— T. anguste oblongo- ^ (^ ^' '^J 



rostrata, compressa, albida, ajquilateralis, undique longitudiualiler 

 striata; striae antiee remotiores. Extremitas rostri attenuati re- 

 curvata, subobHque truncata. j\Iargo dorsalis anticus rectiuscu- 

 lus, vix declivis; posticus valde incurvatus, paululuin declivis. 

 Area magna excavata, carina plicas umboiialis simplici circum- 

 scripta. — Of a much-produced beaked-oblong shape, rather thin, ' 

 compressed, whitish, with a very shallow radiating itidcntation 

 anteriorly, before which the close-set shelving subconcentric striii; 

 that elsewhere traverse the entire surface become more distant. 



