MOLLUSCA OF THE ' CHALLEN&ER ' EXPEDITION. 601 



rounded above, very sharply angulated at the keel, and flattened 

 on the base, with a bluntly angulated umbilical edge. Suture 

 distinct, slightly impressed. Mouth perpendicular, square. 

 Outer lip sharp, thickened by a slight internal remote callus, 

 not patulous, not descending, advancing at its junction with the 

 body-whorl and then slightly retreating so as to form the very 

 shallow open sinus ; right-angled at the periphery, flat on the 

 base, where it retreats so as to form two rounded sinuses, making 

 with the pillar an angle that is scarcely obtuse. Pillar-lip is 

 straight, slightly thickened and reverted, so as to leave a 

 slight groove behind it. It advances on the body-whorl, 

 then retreats so as to form a slight sinus, bending at the same 

 time shortly but sharply to the right into the umbilicus and 

 then advancing straight forward, but a little toward the left, to 

 its junction with the outer lip at the base. JJmhilicus funnel- 

 shaped, open-mouthed, oblique-edged, straight-sided, deep and 

 contracted internally. Its edge is sharply defined by a spiral 

 thread, and is obliquely scored by the longitudinal ribs ; further 

 in its walls are marked by hair-like lines of growth and faint 

 spirals. Height 0-12. Breadth 0*14 ; least O'll. Penultimate 

 whorl 0-23. Mouth, height 0-063, breadth 0-061. 

 This species slightly resembles in sculpture the young of Mar- 

 garita striata, Brod. {=-Trochus cinereus, Couth., nee Da Costa), 

 but in all details of form and ornamentation is very diflferent. 

 From Trochus amabilis, Jeffr., besides the generic features, it 

 differs in the depressed spire, in the absence of the deep-cut suture, 

 in the flatness of the base, and in all the features of minute sculp- 

 ture. 



GrAZA, VF., gen. nov. (ya^a, treasure.) 



Testa trochiformis, plane margaritacea, eleganter cselata, labio retroverso 

 calloque margaritaceo incrassato ; columella torta, directa, antice 

 mucrone angulata, postiee a labio penitus disjuncta, ad regionem 

 autem umbilicalem in pulvinum margaritaceum complanata. Opercu- 

 lum rotundum, membranaceum, tenue, multispirale. 



I wish to express by " plane " the sense of both lucide and 

 penitus, the shell being both on the surface strikingly and through- 

 out its whole substance entirely nacreous. 



Whether this and all the other features enumerated above will 

 prove constant is a question for time to determine. At present 

 a new genus is inevitable ; for this shell, though plainly one of 

 the Trochidse and o£ the Trochocochlea group, cannot possibly be 



LINN. JOUEN. — ZOOLOGY, TOL. XIT. 44 



