REPORT ON THE LAMELLIBRANCHIATA. 199 



bifido. Ligamonti fossa elongata, pone dentem posticum locata. Margo valvarum 

 internus denticulis parvis insignibus circiter quinque antice instructus, postice acutus, 

 inferne anguste complanatus. Cicatrices musculares magate, elongatae. Pallii impressio 

 baud siuuata. 



This small species is a little longer than high, subtriangularly rounded, a trirti' 

 inequilateral, thin, not very glossy, moderately gibbous, semitransparent-white, finely 

 sculptured with the concentric lines of growth. The umbones are minute, acute, pro- 

 duced only a little above the dorsal line, are scarcely incurved, and situated a trifle in 

 front of the centre. The dorsal margin is considerably curved on both sides and 

 descends a long way, forming with the broadly arcuate ventral edge sharply rounded 

 extremities. The hinge-plate is not very strong, and furnished in each valve with two 

 cardinal teeth, of which the hinder in the right valve and the anterior in the left are 

 twice as strong as the others, and conspicuously bifid. These teeth are divergent, the 

 anterior being directed towards the front and the posterior backwards. Behind the 

 latter comes the internal ligament which rests in a narrow oblique groove separated 

 from the tooth by an acute ridge. The inner edge of the valves is remarkable on account 

 of five or six distinct denticles situated about the middle of the front side. The lower 

 part especially towards the anterior end is narrowly flattened, whilst along the hinder 

 dorsal slope the margin is more acute. The muscular scars are long and large, and the 

 pallial line is simple. 



Length 4 mm., height 3f , diameter 2^. 



Habitat. — Station 187, depth 6 fathoms, coral mud; also Station 188, depth 28 

 fathoms, green mud ; also Flinders Passage, at a depth of 7 fathoms ; and finally Torres 

 Strait, in 3 to 11 fathoms. All these localities are near Cape York, at the extreme north 

 of Australia. 



This interesting species is very remarkable on account of the denticulations on tlie 

 front margin, which are very strong for so small and delicate a shell. 



Diplodonta amboinensis, n. sp. (PI. XIV. figs. 12-12a). 



Testa subquadrata, convexa, albida, valde insequilateralis, postice lata, obtusa, 

 mediocriter arcuata, antice angustior, valde arcuata, incrementi lineis tenuibus (hie illic 

 paucis majoribus) sculpta, plus minusve, praecipue latum posticum versus, minute 

 subpunctata. Margo dorsi posticus elongatus, fere rectus, parum declivis, anticus valde 

 descendens, vix curvatus, brevior. Umbones parvi, antemediani, in j longitudinis 

 collocati. 



Length 18 mm., height 15, diameter 10. 



Habitat. — Amboina, Molucca Islands, in 15 to 20 fathoms. 



