REPORT ON THE LAMELLIBRANCHIATA. '245 



oliviicea induta. Superficies nitida, incrementi lineis, in medioque aliis paulo obliquis 

 sculpta. Margo dorsi antieus brevis, leviter deelivis, rectiusoulus, posticus vix oliliquus, 

 levissinie incurvatus. JMargo ventralis late arcuatus antice curvatim ascendeus. 

 Umbones paulo prominentes, latus anterius versus inclinati, in ^ longitudiuis collocati. 

 Lunula augustissima, impressa; area postica angusta, utrinque bicarinata. Linea cardinis 

 gracilis, dentibus numerosis instructa. Pagina interna, nitens, cseruleo-albida, lineam 

 pallii mediocriter profuude sinuatam exliiljens. Ligamentum olivaceo-fuscum, promineus. 



This interesting species is rather thin, convex, markedly inequilateral, of an ol)long, 

 squarish form, especially at the posterior side, which is ol)liquely and slightly arcuately 

 truncate. Down the posterior side two faint depressions radiate from the umbones, the 

 one to the lower rounded extremity, the other to the middle of the truncated side. The 

 epidermis is glossy, thin, of a pale olive tint, and exhibits rather strong lines of growth, 

 especially in front, and on the central portion of the valves other elevated thread-like 

 lines crossing them obliquely. These slanting lines are not present in the early stages 

 oi growth. The front dorsal margin is short, nearly rectilinear, and just a little oblique, 

 the posterior being much longer, nearly horizontal, and verj^ slightly incurved. The 

 lower outline is very gently arcuate, and rises more gently in front than behind. There 

 is a very narrow lunule, which is sunken and well defined. The posterior dorsal area 

 is also narrow, excavated, bounded by a raised slender ridge, and has a slender thread- 

 like keel on each side, mid-way between the central divisional line and the outer ridges. 

 The umbones are a little raised above the dorsal line, incline towards the front, a trifle 

 incurved, and located at about one-third of the entire length of the shell from the 

 anterior end. The hinge-plate is rather slender, and Itears (in the largest specimen 

 under examination) about fifty-five not very long teeth, of which about fourteen are in 

 front of the umbones. The ligament is prominent and of a browTiish-olive tint. The 

 interior is glossy, bluish-white, and on account of the thinness of the shell exhibits more 

 or less of concentric sulcation, corresponding to the external ornamentation. The 

 pallial sinus is moderately deep, not reaching to the centre, and sharply rounded at the 

 end. 



Length 204 mm., height 12^, diameter 8. 



Habitat. — Station 191, near the Arrou Islands, in 800 fathoms; green mud. 



Malletia ohtiisa, G. 0. Sars. 



Malletia obtusa,G. 0. Sars, Moll. Eeg. Arct. Norv., p. 41, pi. xix. figs. 3, a, b. 

 MulJftia ohtusa, Jeffreys, Proc. Zool. Soc. Lond., 1879, p. 586. 

 Yoldla ohtusa, Sars, Remark. Forms Auimal Life, p. 23, pi. iii. figs. lG-20. 

 Yoldia abyssicola, Sars, Porhandl. Vidensk. Selsk. Cliristiania, 1858, p. 86. 



Habitat. — Station 47, south of Nova Scotia, in 1340 fathoms; and Station 45, off 

 the east coast of the United States, in 1240 fathoms. 



