u4 THE VOYAGE OF II.M.S. CllALLEJS'UElt. 



ridges, of which those upon tlie surfece between tlio middle of tlic valves and the 

 commencement of the rostrum are thicker than the rest, those upon the beak itself 

 beiiio- almost obsolete. In addition, it is ornamented with the lines of (irowtli, which, 

 in some places, are so strong as to produce a slightly cancellated appearance. The 

 front dorsal margin is much elongated and a little curved, the posterior, on the contrar)-, 

 being slightly concave and just a trifle oblique. The anterior end is obliquely sloped 

 above, with a very small curve, and terminates in a moderately sharply rounded 

 extremity. The ventral outline forms a broad curve except beneath the rostrated end, 

 where it is feebly sinuated. The beak is broad, rather short, curvedly truncate at 

 the end, and exhibits above, a narrow, slightly sunken dorsal area. The umbones nie 

 moderately large and acute, recurved, somewhat raised above the hinge-line, and 

 located rather in advance of the centre. The hinire mioht be said to l)e toothless, 

 although in the right valve there is a very insignificant ridge, starting from the 

 ligament-pit and continued a little way parallel witli the posterior dorsal margin, M'hich 

 might be regarded as an incipient lateral tooth. The ligament is small, short, and 

 oblique, inclining towards the anterior end. The interior is not very glossy, but 

 exhibits radiating grooves and striae corres2:)on(ling to the external ridges and lira;. 

 The hinder muscular scar is more distinct than the front one, ami Imiilei'ed anteriorly 

 by a thickened ridge. 



Length 20 mm., height 12, diameter 9. 



Habitat. — Off Prince Edward Island, in 300 fathoms. 



This is a large and very fragile species, in many respects similar to Neara ciuia. 

 Jefireys. It is perhaps a little longer in proportion to the height, has more distinct 

 lii-se on the anterior half of the surface, a narrow sunken dorsal area, and lacks the 

 *' short strong triangular lateral " tooth on the posteiior side of the ri-ht Aahc wliicli 

 occurs in that species. 



Puroiiii/a, Forbes. 



Poromya australis, u. sp. (PI. XI. figs. 2—26). 



Testa parva, aequilateralis, tenuis, albida ; margo dorsi utrinquc valdc declivis, 

 antice concaviusculus, postice Icviter convexus. Valva dextra mediocriter convexa, in 

 regione lunulari concave depressa, prope marginem dorsalem posticum carinata, undique 

 granulata, granulis confertis, erectis, in quincuncibus digestis. Umbo prominens, ad 

 apicem levigatus, antrorsum versus. Dens cardinalis unicus validus, erectus, infra 

 apicem locatus. Pagina interna alba, nitida, leviter margaritacca. 



Only a single right valve of this species was obtained. It is al)out as long as high, 

 rounded at both ends, and along the ventral margin it is more gentl}' curved. It is 



