26-t THE VOYAGE OF H.M.S. CHALLENGER. 



posterior side, marking oft' as it were a dorsal area. The umboiies are very promiueut, 

 much inflated, well curved over towards the front, and a little remote from one another. 

 The anterior outline is oblique, In-oadly and somewhat irregularly arcuate, there being a 

 slight bulge near the upjier extremit}-. The posterior side is straighter, very faintly 

 sinuated liy tlie radiating depression, and regularly rounding beneath into the ventral 

 margin, which- is obliquely subsemicircular. The dorsal area is narrow, broadest in front 

 of the ])eaks, gradually attenuating posteriorly. It has the central line elevated 

 anteriorl}", and sunken at the opposite end beneath the ligament. This is small and of 

 course narrow, bounded on each side by the acute raised edges of the area, of a black 

 colour, and located in a few parallel grooves forming a much elongated diamond-shaped 

 figure. The hinge-line is slender, almost equalling the shell in length, and armed with 

 a few rather irregular teeth, at times more or less obsolete near the centre. The 

 interior of the valves is white, and on account of the thinness of the shell partly exhibits 

 the character of the external sculpture, and is more or less radiately faintly punctate, 

 the rows of minute feeble pittings corresponding with the lir^e of the exterior. 



Length 20 mm., height 25, diameter 19^. 



Habitat. — Station 184, east of Ca2)e York, Noi'tli Australia, at a depth of 1400 

 fathoms ; Station 194, south of Amboina, in 200 fathoms ; Station 198, oft" the north- 

 eastern extremity of Celebes, at a depth of 2150 fathoms; Station 216a, north-west 

 of New Guinea, in 2000 fathoms; Station 271, Mid Pacific, depth 2425 fathoms; 

 and finally. Station 300, near the Island of Juan Fernandez, off the Chilian coa.st, in 

 1375 fathoms. 



This species is very unlike the typical forms of Barhatia, being far more globular, 

 of very thin substance, more finely sculptured, and clothed with a thinner epidermis. 

 There are, however, intermediate species which it more nearly resembles in some of the 

 above mentioned particulars, s(j that I think it may (at all events for the present) be 

 considered a very aberrant form of that group. 



Area [Acar) congenita, u. sp. (PL XVII. figs. 6-6a). 



Testa oblonga, crassiuscula, insequilateralis, antice angusta, oblique curvata, postice 

 latior, oblique truncata, superne inferneque angulata, albido-fuscescens, lamellis eoncen- 

 tricis, crassis, liris radiantiluis minus conspicuis crenulatis, sculpta. Valva? jjone 

 angulum cristatum al) umbone ad extremitatem posticam decurrentem concavse, in medio 

 leviter depressse. Umbones parvi, parum remoti, circa in f longitudinis coUocati. Area 

 ligament! angusta ; dentes ad sedecim utrinque ol)liqui. Pagina interna alba, subnitida. 



This is a fairly solid little species, whitish l)rown, very inequilateral, of an oblong 

 form, narrow in front and gradually widening towards the posterior end, which is 



