REPORT ON THE LAMELLIBRANCHIATA. 277 



This species luis been recorded iruiii Cuba (Philipiii) ; Jamaica, Martinique, 

 Guadaloupe, and St. Domingo (d'Orbigny). 



Lithodomus nudaccanus, Reeve. 



Litliodomng maluccanit-i, Reeve, Conch. Icon., vol. x. pi. iv. li^'. 20. 

 Lithophaga malaccana, Dunker, Conch. -Cab., ed. 2, p. 20, pi. v. ii". I. 



Habitat. — Station ISG, off Cape York, North Australia, in 8 fathoms. 



The anterior end of this species is rounded, but the hiuder extremity of the shell, 

 which can only be seen when tlie valves are parted, is more truncate and only a little 

 arcuate. The interior is of a pale brown tint, and more or less iridescent. 



Subfamily Crenellin/J';. 



CretieUa, Brown. 



Crenella marioneasis, n. s]i. (PI. XVI. figs. G-Qa). 



Testa parva, tenuis, alba, nitida, paulo obliqua, subcordata, convexiuscula, superne 

 hita, inferne angustata, radiatim tenuiter lirata, liris incrementi striis decussatis. 

 Umbones rotundati, vix elevati, ad apices obtusi, semipellucidi. Linea cardinalis angusta, 

 minutissime transversim striata, in medio, infra umbonem fossa ligamenti curvata 

 transversa insculpta, prominentia dentiformi laterali postica in valva sinistra instructa. 

 Pagina interna subnitens, umbones versus minute subpunctata, inferne radiatim tenuiter 

 sulcata, ad marginem subtiliter denticulata. 



This is a very thin, delicate species, white, glossy, and sculptured with numerous fine 

 radiating lirse which are scarcely raised at all and crossed by the concentric lines of 

 growth. This ornamentation is so fine that it is all Init invisible to the naked eye. 

 The form is oblique, somewhat cordate, rather convex, l)roader above towards the 

 umbones than at the lower end. The posterior side is regularly broadly curved in an 

 oblique direction, the anterior being more erect and straighter. The umbones are 

 moderately large, not much elevated, and terminate in a rounded semipellucid tip. The 

 liinge-plate is narrow, microscojjically transversely striated, has an elongate, narrow, 

 central ligamental groove and a single more or less distinct lateral tooth-like projection 

 on the hinder side in the left valve, and an indication of one in the right. The interior 

 of the valves under the microscope appears towards the uml>ones to be subpunctate, 

 and is finely striated towards the minutely dentate margin. 



Length 4 mm., height i^, diameter 2f. 



Habitat. — Station 145, ofi" Marion and Prince Edward l.-lands, in 140 fathoms. 



