8G THE VOYAGE OF H.M.S. CHALLENGER. 



valve's surface, and consequently bounded by an acute edge extending from the umbo 

 almost to the posterior extremity of the shell. In front there is a shallow elongate 

 lunule, but not strongly defined. The umboncs are small, acute, and just prominent 

 above the hinge-line. The two cardinal teeth in the right valve are about equal in size, 

 diverge from one another, being united at the upper extremities. The anterior slopes 

 towards the front, and the posterior in the opposite direction. The lateral grooves for 

 the reception of the side teeth in the left valve are rather remote from the apex, and the 

 posterior one does not extend to the umbo, being interrupted by the margin which 

 borders the internal ligament. This is narrow, elongate, and placed in a very oblique, 

 deep pit, subparallel with the posterior slope. The adductor scars are somewhat pyriform, 

 the hinder one being the broader. The siphonal inflection is very deep, extending some 

 distance beyond the middle of the valve, and is rather acuminate at the anterior 

 extremity. The interior is glossy and indistinctly radiately substriated. 



Length 15^ mm., height 9 J, diameter about 4. 

 • Habitat. — Station 122, off Pernambuco, Brazil, at a depth of 350 fathoms ; red mud. 



This is a more compressed species than Scmele (Abra) lohiUppinensis, with straighter 

 dorsal margins, and at once distinguished by the flat posterior area. 



Semele (Abra) philippinensis, n. sp. (PI. V. figs. 3-3(i). 



Testa tenuis, subdiaphana albida, zonis pellucidis hie illic oruata, concentrice tenuiter 

 striata, subsequilateralis, transversim elongata, antice rotundata, postice valde acuminata, 

 utrinque angustissime hians. Lunula angusta, lanceolata, baud profunda. Valvarum 

 pagina interna laevigata, superue prope umbones minute corrugata. Sinus pallii latus, 

 profundissimus. Dentes cardinales valvse dextrse duo insequales, sinistrse tantum unus, 

 laterales pi'ominentes, ab apicibus modice remoti. 



This shell is transversely elongated, more than one and a half times as long as high, 

 sharply rounded in front, and acuminate posteriorly. It is thin, somewhat gaping at 

 each end, not very compressed, semitransparent, glossj^ ornamented with alternate 

 opaque and diaphanous concentriczones, the former being the broader, and sculptured 

 with very fine lines of growth. The dorsal outline is sul)rectilinear posteriori}^, and 

 obliquely descending, in front being all but horizontal, feebly concave close to the beaks 

 in the region of a small lanceolate lunule, and then faintly arcuate. The ventral margin 

 is very broadly curved, and more ascending at the anterior than the opposite extremity. 

 The umbones are small, a little post-median, but slightly elevated, and turned very slightly 

 towards the front, and are nearly in contact. The two cardinal teeth in the right valve 

 are unequal in size, diverging, and situated in front of the narrow and very oblique 



