REPORT ON THE LAMELLIBRANCHIATA. 205 



nearly equilateral, moderately convex, and lias l)ut little gloss upon the surface. The 

 dorsal margin is not much curved near the umbones, but gradually rounds off into the 

 sides, and the ventral outline is regularly widely arcuate, and a little more ascendant 

 posteriorly than in front. The umbones are not very acute, central, and just a little 

 raised above the hinge-line. Tlie divergent lateral tooth on each side in the right valve 

 is prominently raised, there being a wide triangular space between them under the umbo. 

 The interior is not highly glossy, but exhibits traces of faint radiating striae, principally 

 towards the margin. The muscular scars are deep, shining, and united by a simple 

 distinct pallial line. 



Length 5^ mm., height 4, probable diameter of a perfect specimen 2|. 



Ilahitat.^-'Povt Jackson, New South Wales, in 2 to 10 fathoms. 



Unfortunately only a single right valve of this species was dredged. It is, however, 

 of sufficient importance to merit description, as it appears to be an addition to the fauna 

 of Port Jackson, the MoUuscan portion of which has been catalogued and described by 

 my friend G. French Angas, after whom I have named the species. 



Montacuta acuminata, n. sp. (PI. XII. figs. 3-3/>). 



Testa parva, tenuis, semitranslucida, vitreo-alba, nitida, incrementi liueis tenuissime 

 striata, subsequilateralis, ovato-triangularis, utrinque aliquanto acuminata, postice breviter 

 subrostrata. Margo dorsi utrinque valde declivis, antice leviter arcuatus, postice 

 rectiusculus. Margo inferior late curvatus, latus posticum versus hand profunde 

 sinuatus. Umbones parvi, acuti, fere mediani. Dentes valvee dextrjB duo, quorum 

 anterior prope umbonem locatus, posterior magis remotus, elongatus. Pagina interna 

 nitida, radiatim substriata. Sinus pallii mediocriter magnus, latus. 



This species is rather triangular, being acutely rounded in front and shortly beaked 

 behind. It is very thin, semitransparent, hyaline, marked only by very fine lines of 

 growth, rather inflated, and almost equilateral. The dorsal outline is very sloping on 

 both sides of the beaks, the angle of divergence being about 108°. On the anterior side 

 it is slightly excurved, but behind is nearly straight and sharply bent at right angles to 

 the surface of the valves, formingr a flat linear dorsal area. The ventral margin bulges 

 somewhat at the middle, gently curves upwards anteriorly, and exhibits behind a faint 

 sinuation. The beaks are about central, small and acute. The left valve possesses no 

 teeth, and displays merely a slight thickening of the dorsal edge, ju.st in front of the 

 apex. The scar of the internal ligament in this valve is oblique, and under the posterior 

 dorsal margin near the uml:)o. In the right valve there are two teetli, the one thin, shortish, 

 erect, close to, but in front of the umbo, the other more remote and longer. The interior 

 of the valves is glossy, faintly concentrically grooved near the lower margin, and more or 



