228 THE VOYAGE OF H.M.S. CHALLENGEE. 



incurved at the tips, ;iiid situated consideraMy iu front of the middle. Tlie interior i.s 

 pearly white, and the inner edge of the valves smooth. The hinge-plate is moderately 

 strong, and furnished with ten or eleven stoutish teeth, six of which on the posterior 

 side are larger than the four or five on the opposite margin. 



Length 3 mm., height 2^, diameter 1 



Habitat. — Station 120, off Peruamhuco, Brazil, in 675 fathoms; red mud. 



The few small valves here described bear considerable resemblance to Niicula corhii- 

 loides of Seguenza, a Tertiary fossil from Italy, but are, I believe, distinct ; for, besides a 

 difierence in form, the surface cannot be described as " Isevis, lineis incrementi paucis 

 siguata" (Seguenza), the concentric strias in the present species being regular, numerous, 

 and even strong for so small a shell. 



Nucula culebrensis, n. sp. (PI. XVIII. figs. 11-11((). 



Testa subcompressa, medioeriter crassa, valde incequilateralis, ovato-trigoua, con- 

 centrice tenuissimc lirata, uudique radiatim striata, postice serie arcuata jirope marginem 

 dorsalem tuberculorum compressorum in utraque valva ornata. Margo dorsi posticus 

 elongatus, declivis, subrectus, anticus brevior, vix excavatus. Lunula et area postica 

 distinctse. Dentes cardinis eirciter vio'inti. Pamna interna alljo-marjxaritacea, marffine 

 inferiori intus tenuiter crenulato. 



This species is ovately trigonal, sharply rounded at each end, rather compressed, very 

 inequilateral and moderately solid. It is sculptured with numerous fine concentric 

 liree and closely packed minute radiating strije, chiefly visible in the intervening grooves, 

 and near the posterior dorsal margin in both valves some of the concentric lir£e are 

 thickened at the ends, forming a series of compressed tubercles, which mark ofi" a smooth, 

 lanceolate, posterior area. The dorsal margins meet almost at a I'ight angle, the posterior 

 being nearly straight, and the anterior also straight or very slightly concave. The 

 ventral margin is gently curved. The umbones are small and curved over towards the 

 front over an indistinct, small lunule, beyond which a faint groove radiates from the 

 beaks to the anterior extremity. The hinge-teeth are moderately strong, about twenty 

 in number, of which seven or eight are in front of the beaks and the rest behind. The 

 interior is pearly white, and the lower margin is minutely crenate within. 



Length 6 mm., height 5, diameter 3^. 



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



Only dead white valves were obtained, so it is impossible to describe the ej^idermis, 

 which, however, in all probability, was of an ordinary character. The chief characters 

 of this species are the concentric lirse, the radiating striae, and the tubercles down the 

 posterior slopes. 



