EEPORT ON THE LAMELLIBRANCHIATA. 67 



direction. The microscopic sculpture is finer at the extremities than on the central 

 portion of the valves, where the radiating striae are clearly developed. The umbo is acute, 

 dii-ected towards the hinder end, and curves over towards the left valve. The pallial 

 sinus is fairly deep and acutely rounded at the end, and is touched by an impressed ray 

 descending from the beaks. The hinder muscular scar is cii-cular, rather high up, aud 

 larger than the anterior, which is a trifle lower down aud subpyriform. The hinge-line 

 and ligament pit are normal. 



Length 6|- mm., height 4i. 



Habitat. — Stations 187 and 188, Iwth iu the region of Torres Strait, North Australia, 

 at depths of 6 and 28 fathoms. 



This species is even more elongate than Myodora. oblonga, in addition to which it is 

 more finely ridged and less acutely beaked at the apex. Myodora pandoriformis is also 

 shorter and more finely microscopically sculptured. 



Myodora australica (Reeve). 



Thraeia wustralica, Eeeve, Conch. Icon., fig. 1-3. 



Tliracia novu-zelandica, Eeeve, Couch. Icon., fig. 19. 



Thraeia novo-zelavdien, Hutton, Manual Moll. New Zealand, p. 136. 



Habitat. — Port Jackson, Sydney, in 2 to 10 fathoms (Challenger) ; Moreton Bay 

 (Reeve) ; Port Jackson (Angas and Voyage of the " Rattlesnake," in the British Museum). 



This, like all the species of the genus, is inequivalve and white, and sculptured with 

 microscopic concentric stride which are interrupted by others radiating irregularly from 

 the umbones, producing a shagreened surface. It is much longer tlian high, somewhat 

 trigonal, acuminate anteriorly, and truncated behind. The right valve is moderately 

 convex and larger than the left, which is much flatter. Both are marked with subplicate 

 lines of growth, and have a slight arcuate angle running from the beaks to the lower 

 posterior extremity, behind which the surface is somewhat concave. The front dorsal 

 margin is elongate, moderately sloping, and very slightly arcuate, the posterior being not 

 quite so oblique, shorter, a little excavated near the umbones, and then straightish. The 

 ventral outline is very gently curved, forming a rounded angle at its junction with tlio 

 posterior side, and joining the anterior dorsal slope in a sharp curve. The umbones are 

 acute, and the area is lanceolate, excavated, and defined by sfight ridges. The dorsal 

 margins of the left (flattened) valve are acute, but at right angles to the rest of the 

 surface, and act as lateral teeth, fitting into corresponding grooves in the other valve. 

 The ligamental scar beneath the beaks is narrow, rather small, moderately deep, and slopes 

 a little towards the posterior end. The anterior scar is long and narrow, the hinder one 

 being shorter and ii-regularly rounded. The sinus in the pallial line is large, deeper than 

 high, rounded at the end, and not extending to the centre of the valves. The internal 



