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



Yoldia, Moller. 



Yoldia lischkei, u. sp. (PI. XX. figs. 4-4?>). 



Testa niedioeriter couvexa, tenuis, paulo iusBquilateralis, oblonga, utriuque hians, 

 autice acute rotundata, postice sursum subrostrata et radiatim baud profuude impressa, 

 iiicremeuti liueis teuuibus, bic illic paucis fortioribus, sculpta, epidermide flaveseeuti- 

 olivacea, colore saturatiori sparsim zonata, amicta. Margo dorsi anticus declivis, leviter 

 arcuatus, posticus longior, fere borizontalis, paulo concavus. Margo ventris late 

 arcuatus, integer. Lunula elongata, angusta, impressa, in medio prominens. Area 

 postica latior, in medio producta, margine acuto cii-cumdata. Umbones parum elevati, 

 ])aulo antemediani, postice inclinati. Linea cardinalis mediocriter fortis, dentibus 

 uumerosis erectis instructa. Fossa ligamenti lata, baud profunda, inferne arcuatim 

 marginata. Pagina interna alba, concentrice plus minusve pellucido-cseruleo zonata. 

 Sinus pallii profundus, latus, rotundatus, paulo ante medium extendens. 



Length 29 mm., height 17, diameter 11. 



Habitat. — Station 232, off luosima, Japan, in 345 fathoms ; green mud. 



This species very closely resembles Yoldia japonica of Adams and Reeve, but is, 

 1 think, distinct. 



That species is a smoother shell, of a paler colour, more convex, more inequilateral, 

 the posterior side being longer in proportion to the anterior ; also it is not so high, and 

 consequently has a longer and more cylindrical appearance. The present species has a 

 faint radiating depression down the hinder side, which does not exist in Yoldia 

 japonica, the posterior dorsal area is more prominent along the middle, and the 

 ligament-pit is broader, not so deep, and less projecting inwards. From a conchological 

 point of view, the genera Leda and Yoldia appear to pass gradually into one another, 

 the extent of the gape at one or both ends, the depth of the pallial sinus, &c., varying 

 to any extent in a large number of species. 



Yoldia isonota, Martens (PI. XX. figs. 5— 5&). 



Yoldia isonota, Martens, Sitzungsb. Gesellscli. naturf. Freimde, Berlin, 1881, p. 79. 



Testa transversa, convexa, sequilateralis, antice acute rotundata, postice superne 

 subnasuta, in medio sinuata, impressione radiante notata, incrementi lineis costiformibus 

 in impressione posteriori flexuosis sculpta, epidermide crassiuscula, flavo-olivacea, supra 

 costellis saturatissima, induta. Margo dorsi utrinque vix declivis, postice rectus, antice 

 levissime excurvatus. Margo ventralis late arcuatus. Lunula nulla. Area postica 

 aliquanto indistincta, leviter impressa, elongata, angusta. Linea cardinis mediocriter 

 valida, dentibus ad septendecim acutis utrinque munita. Fossa ligamentalis profunda, 

 paulo intus projecta. Pagina interna nitida, iridescens, albido cjeruleoque zonata, plus 

 minusve flavo tincta. 



