NucuLiD^;. 23 



conspicuc recurvata. Margo dorsalis aiiticu vix declivis, postice 

 bis incurvatus ; vciitralis in medio maxiiiic arcuatus, utrinque 

 niultum acclivis. Are?e dorsales haud iiisculptse; anfica incon- 

 spicua ; j)ostica concaviuscula, et su!co lato profundo circumscripta. 

 — Beaked-ovate, veiitricose or tumid, only (yet much) gaping at 

 tlie hinder tip, of a polislied ivory-white, with a very faint anterior 

 indented ray, ck)sely grooved lengthways throughout ; the sulci 

 shelving, except upon the beaks and near and upon the feebly 

 developed umbonal ridge, where they become broader and square- 

 cut, and their intervals form costellae. Anterior extremity rotun- 

 dately subangulated above, obli(|uely rounded below. Posterior 

 side attenuatcdly beaked, its tip, which is contracted at its origin 

 both above and below-, very narrow (yet blunt), peculiarly upturned 

 (in the adult), and above the middle. Front dorsal slope very 

 sligiit, straightish or plano-convex : hinder dorsal slope witli a 

 double incurvation. Ventral margin much arcuated in the middle 

 and front, straighter behind, much rising at both ends, slightly 

 retuse near its posterior termination. Dorsal areas smooth or 

 nearly so : the front one inconspicuous ; the hinder one plano- 

 concave, environed by a deep, broad sulcus, which angulates its 

 sides, and makes it appear raised. — Under a powerful glass, a few 

 radiating lyrse may be descried near the commencement of the 

 indented ray : they are best seen in the younger individuals, which 

 are usually pale fulvous, and do not display the cocked-up beak, 

 being merely acuminated to a subcentral tip (Rec. Biv. pi. 19, f. 46). 

 39. L. PUELLATA, Hhiih, f. 94. — T. perparva, subscquilateralis, 

 obovato-acuta, antice late rotundata, in medio tumida, postice 

 compressa et repente recurvato-acuminata ; alba, oculo armato 

 antice inclinato-sulcata, postice arctius sulco-costellata, radii im- 

 pressi expers, plica umbonali planulata, sed utrinque angulari, 

 munita. Margo dorsalis antice vix declivis, postice retusus de- 

 clivisque ; ventralis antici"; multum arcuatus, posiice rectior et 

 multum acclivis. Area angulatim defiuita, duplex ; interior pla- 

 nulata, iaevis, linea carinatii circumscripta. Lunula inconspicua. 

 — Small, pcakcd-obovate, suhequilateral, tumid in the middle, 

 comjjressed behind, white, devoid of a coloured epidermis or an 

 anterior indented ray ; smooth to the eye, but under the lens most 

 closely and finely (the dorsal areas excepted) suleato-costellated ; 

 umbonal ridge planulate, subcarinately angular on either side. 

 Front extremity broadly rounded : hinder extremity abruptly 

 acuminated ; the tip upturned, rather above than below the middle. 

 Front dorsal slope slight, plano-convex. Hinder dorsal slope 

 moderate, retuse. Ventral margin much arcuated in the middle 



