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



interruptim eoncentrice striata, Margo dorsi utriiifjiie valde deseendens, subsequalis, 

 posticus rectiliuearis, anticus levissime couvexus. Margo ventralis late arcuatus, postice 

 Adx adsceudeus. Sinus pallii arcuatus, minime profundus. Pagina interna sulco radianti 

 unico notata. 



There is but a single left or flat valve of this species in the collection. It is 

 triangular, nearly eqiiilateral, acute in front, shortly truncated posteriorly, a little 

 concave, concentrically grooved and lidged, the ridges being nearly obsolete behind an 

 impressed ray which runs from the acute umbo to the lower angle of the hinder trunca- 

 tion. The dorsal margins are about equal in length, and converge at an angle of about 

 60°. The hinder is c[uite rectilinear, except just behind the umlio, where there is the 

 faintest incurvation, the anterior being, on the contrary, slightly excurved. The lower 

 margin is ^videly arcuate, a little up-cur\'ing in front, and scarcely at all at the opposite 

 end. The internal surface is glossy, porcellanous, and marked with a single radiating 

 groove, extending from near the acute recurved beak to the side of the shallow sinus in 

 the pallial line. 



Leno-th 7 mm., heio-ht 51. 



Habitat. — Flinders Passage, Cape York, North Australia, in 7 fathoms. 



The single valve here described approaches il/yoc?oro trigona,liieeYe. It is, however, 

 distinguished by the longer straight posterior dorsal slope, greater concavity of the 

 surface, and the more pronounced radiating groove. 



Myodora sp. 



Testa elongata, tenuis, paulo infequilateralis. Valva dextra mediocriter convexa 

 postice pone porcam radiantem ab uml)one ad extremitatem posticam decurrentem 

 ali(|uanto excavata, eoncentrice lirata, latere, antico rotunde subangulato, postico oblif^ue 

 truncate. Margo dorsi anterior obliquus, fere rectus, posticus paululum longior, leviterque 

 concavus, declivis. ]\Iargo ventralis latissime arcuatus. Sinus pallii modice profundus, 

 apice subacuto. 



Only two right valves of this .species were obtained. They are very elongate, thin, 

 a Uttle inecjuilateral, finelj^ and subdistantly costate, the ridges disappearing at the 

 arcuate angulation which marks off a small depressed portion of the surface at the hinder 

 end. The dorsal margins are subequally oblique, and form at the umbo an angle of about 

 65°. The posterior is slightly the longer, and a little concave, the anterior being nearly 

 rectilinear. 



The lower margin is very gently curved, and forms with the dorsal slope an acutely 

 rounded anterior extremity, the opposite end being broadly truncate in a slightly oblique 



