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



curved, sometimes, but uot always, with the faiutest trace of a sinus behiud, 

 indicating a \'ery inconspicuous radiating depression upon the surface of the valves. 

 The umbones are prominent, smooth, incurved, directed towards the front, and situated 

 considerably^ in advance of the centre. There is neither lunulc nor posterior area. The 

 hinge -plate is fairly strong, broader in front than behind, and supports an unbroken 

 series of about thirty teeth, of which ten are anterior to the beaks. The central 

 denticles are small, Ijut the laterals are fairly long and acute. The ligament is placed 

 in a small narrow groove above the teeth, just behind the apices. The scars and 

 pallial line are indistinct. 



Length 5 mm., height 4, diameter 3. 



Habitat. — Station 24, ofFCulebra Island, West Indies, in 390 fathoms; Pteropod ooze. 



This is a much more slender species than MaUetia veneriformis, much narrower 

 posteriorly, and more finely sculptured. The hinge-characters of both, however, are 

 alike. 



Family A R c i D .e. 



Subfamily PectunculixvE. 



Glom us, Jeffreys. 

 Glomus nitens, Jeffreys. 



Glomus nitens, Jeffreys, Ann. and Mag. Nat. Hist., 1876, voL xviii. p. 433. 

 Glomus nitens, Jefifreys, Proc. Zool. Soo. Lond., 1879, p. 573, pi. xlv. fig. 5. 



Habitat. — Station 323, off the Ptio de la Plata, in 1900 fathoms ; blue mud. 



This species has been recorded liy the late Dr. Jeffreys from several stations in the 

 North Atlantic, at depths of from 500 to 1750 fathoms, but this is its first occurrence 

 so far south. 



The cartilage is placed in a narrow groove parallel with the hinder dorsal margin, 

 AA'hich extends from the umbones a short distance under the teeth on that side. 



Glomus jeff're y si, n. sp. (PI. XXI. figs. 1—1 6). 



Testa minuta, teuuissima, mediocriter convexa, sequilateralis, subcii'cularis, postice 

 oblique subtruncata, ibique impressione radiante baud profunda exhibens, albo-peUucida, 

 nitida, incrementi lineis tenuissimis sculpta. Umbones pai-va, paulo supra margiuem 

 projecti, baud acuti. Linea cardinis mediocriter valida, dentibus cireiter sedecini 

 (quorum sex ante medium cseterique postmediani sunt) instructa. Ligamentum 

 Langustum, in fossa obliqua umbones infra locatum. 



