50 THE VOYAGE OF H.M.S. CHALLENGER. 



of the valves is sliallowly radiately grooved towards the posterior end, and exhibits a 

 moderately strong supporting ridge beneath the iimlio. 



Length 7 mm., height 5, diameter 3;^. 



Habitat. — ^Station 185b, east of Cape York, in 155 fathoms ; coral sand. 



Section E. 



NecBva teres, JefFre5-s (PI. X. figs. 3-3&). 



Xewra teres, Jeffreys, Proc. Zool. Soc. Lond., 1881, p. 939, pi. Ixxi. fig. 2. 



Testa tenuis, semipellucido-albida, serica, giobosa, rotundato-triangularis, postice 

 breviter rostrata, sequivalvis, sequilateralis, ad extremitatem posticam hians. Margo 

 dorsi anticus declivis, vix excurvus, posticus oblic^uus, concavus. Ventris margo late 

 arcuatus, prope rostrum leviter sinuatus. Valvse concentrice tenuiter striatge, carina 

 obliqua, filiforme, radianti, I'ostrum dissecante, ad iustructae, liriscjue paucis aliis 

 teuuibus radiantibus inter carinam et marginem dorsi ornata3. Umbones nitidi, 

 mediocriter elevati, mediani, apicibus antice versis. Denies cardinales nuUi. Laterales 

 duo in valva dextra breves, lamelliformes, valde prominentes. Ligamentum obliquum, 

 latus posterius versus incliuatum, in loculamento insigne, postice acuminato, in. 

 valva .sinistra situm. Paoina interna nitida, radiatim striata. Cicatrix anterior 

 parva, postica major, porca rotundata valida intus marginata. 



This species is rather globose, triangularly rounded, shortly beaked, and gaping 

 behind, thin, semitransparent-white, and exhiliits towards the lower outline, and upon 

 the rostrum, more or less of a thin fibrous epidermis. The valves are equal and have a 

 silky appearance, being sculptured with fine strias of growth. The beaked portion 

 terminates in a short curved truncation, and is divided down the middle by an oblique, 

 slightly arcuate thread-like carina, extending from the umbo to the lower end of the 

 rostrum. Between this keel and the dorsal margin, the surface is ornamented with a 

 fewer, finer, and less conspicuous radiating lirse, which are crossed by rougher lines of 

 growth than those upon the rest of the shell. The dorsal margin is moderately oblique 

 on both sides, being nearly rectilinear in front, and gently concave behind. The anterior 

 end and ventral outlines are regularly curved, but the latter, behind, under the rostrum, 

 is just faintly incurved or sinuated. The umbones are fairly raised, glossy at the tips, 

 which are curved over towards the front and situated midway between the extremities 

 of the shell. The right valve has a very prominent lamellar lateral tooth on each side 

 rather near to the apex, the posterior, after being suddenly truncate behind, is continued 

 in the form of a slightly elevated ridge, immediately under the dorsal margin, some 

 distance along the rostrum. There are no cardinal teeth in either valve. The left 

 valve has the margin thickened on both sides, especially in front of the umbo, near 



