954 PELECYPODA. [Eulamellibranchia. 



rounded, somewhat straightened in the middle. Sculpture consisting 

 of close and fine concentric striae with distinct periods of rest ; the 

 strise are more distinct and slightly raised on both ends, inconspicuous 

 in the centre ; very faint and distant radiate lines are visible under a 

 good lens. Epidermis very thin, yellowish, easily rubbed off. Colour 

 yellowish-white, darker on and above the posterior fold. Interior 

 white, porcellanous ; margins smooth. Hinge : Right valve with a 

 central triangular and bifid cardinal, a second, smaller and oblique, in 

 front of it ; close and parallel to it is a distinct lateral tooth ; a trace 

 of a posterior lateral is mostly present, situate behind the nympha, 

 the latter being rather short ; left valve with a posterior, thin and 

 very oblique, and a central, trigonal, bifid cardinal. Ligament rather 

 short and high. Anterior adductor-scars oval, posterior scars almost 

 round and larger. Pallial sinus large, broadly triangular, the highest 

 point near the middle of the antero-posterior axis, thence descending 

 to within a short distance of the anterior adductor-scar ; the ventral 

 part coalescent with the pallia! line. A radial ray passes from the 

 beaks towards the margin behind the anterior adductor-scar, and 

 2 posteriorly, all of which, however, are not very conspicuous. 



Length, 45 mm. ; height, 25 mm. ; diameter, 10 mm. 



Type in my collection. 



Hob. North and South Islands : Opotiki. type (C. Spencer) ; 

 Hicks Bay (Captain Bollons) ; New Brighton and Akaroa Harbour, 

 in 6 fathoms (H. S.). 



Genus 2. MACOMA, Leach, 1819. 



Macoma, Leach, App. ii, Ross's Voy., p. Ixii, 1819. Type : Macoma tenera, 

 Leach (= Tellina calcarea, Gmelin). Limicola, Leach, 1852; not of 

 Koch, 1816. Macalia, H. Adams, 1860. Tellinungula, Romer, 1872. 

 Capsa, Tryon, 1869. Psammobia (sp.), Turton, 1822. Psarnmotea, 

 Gray, 1847 ; not of Turton, 1822. Sanyuinolrtria (sp.), Conrad, 1831. 

 Rexiihcerus, Conrad, 18(>9. 



Animal having the siphons naked, the anal siphon long, the bran- 

 chial siphon very short. 



Shell subtrigonal, the periostracum conspicuous, with a marked 

 posterior flexure, usually colourless, or, if coloured, without a colour 

 pattern ; hinge without' lateral teeth ; right valve with 2 convergent 

 cardinals, the posterior larger and cleft ; left valve with an anterior 

 larger slightly cleft cardinal, and on the nympha a smaller cardinal, 

 which sometimes becomes obsolete ; in adult shells one or the other 

 of these teeth, or all, disappear. The pallial sinus coalescent with 

 the pallial line below, and often discrepant in the two valves. 



Distribution. All seas. Typical forms inhabit mostly the cooler 

 seas, and especially boreal waters ; in the laminarian and coralline 

 zone. 



Fossil in the Tertiarv. 



