39 



Like M. trossulits or small specimens of M. edulis in form, but much 

 more elongated. The diverging furrows are quite coarse and obvious 

 in some specimens, and in others obsolete ; the fine striation in the 

 neighborhood of the byssus may always be seen. 



Septifer furcillata. T. parvula, pyriformis ; margine liga- 

 mentali angulatil, compressa, ; declivitate umbonali elevata ; facie 

 ligamentali latfi, margine recta; sulcis quadratis divergentibus con- 

 cinne clathratis insculpta, sulco mediano et sulco subventrali majori- 

 bus, ex quibus sulci versus marginem recurvati exoriuntur. Long. 8 ; 

 lat. et alt. 4 millim. Inhabits China Seas. W. S. 



A somewhat worn valve furnishes the above description, which I 

 venture to give because the sculpture is so peculiar. It has the form 

 of aS". Cumingii, but a much coarser sculpture. 



Pectex l^tus. T. rotundato-ovata, convexiuscula, vivide rufa ; 

 auricula parva fere rectangulari ; a. altera duplo longiori, acutangu- 

 lari, extremitate arcuata ; sinu byssali magno ; valvse integras costis 

 10-12 majoribus laminas remotas erectas fornicatas gerentibus, 3-4 

 minoribus plus minusve muriculatis interpositis ; v. altera costis fre- 

 quentioribus minoribus squamigeris, costulis muriculatis interpositis ; 

 auriculis (nisi area ad sinum tendente) radiis numerosis spinulosis 

 munitis ; cavositas valva; integrae rubricata ; v. alterre pallidior, fere 

 alba. Long. 3.5 ; alt. 3.75; lat. 1.5 poll. Inhabits Hakodadi Bay, in 

 shelly mud, 10 fath. W. S. 



Resembles generally /^ senatorius^ but is more elongated, the small 

 ear longer, and the ribs much less regularly disposed. It is still more 

 like P. cauriniis G. in whicli the ribs are angular and more regularly 

 disposed. In old and heavy specimens the scales are worn off; and 

 in some young specimens, too, they are inconspicuous. 



OsTRKA RivuLARis. T. discoidca, subcircularis, tenuis ; valva 

 inferior crassior, purpurasceus, costis radiantibus remotis, interruptis, 

 subtubulosis munita ; v. superior simplex, rivulis ramosissimis purpur- 

 ascentibus venosa : cavositas minime profunda, ovata, alba cinereo 

 late marginata ; cardine debili. Diam. 60; lat. 10 millim. Inhabits 

 the China Seas, as indicated by shells adhering to it. 



The rays of little tubes below, and the veins above, are unusually 

 clear, distinctive characters. 



Plicatula simplex. T. parva, solida, cinerea vel rubida, flabelli- 

 formis, symmetrica, quadrantem baud asquans ; marginibus rectis, 

 planulatis ; costis praecipuis 6 et costulis numerosis laterahbus, etiam 

 laminis concentricis numerosis munita. Long. 15 ; lat. 8 millim. 

 Common at Kagosima Bay and Simoda, 5-20 fath. W. S. 



Placunanomia umbonata. T. discoidea, talcosa, fragilis, admo- 

 dum levigata, straminea : valva superior obsolete radiata, et umbonem 



