308 Mr. A, Adams on new Genera and Species of 



menti concentricis ad tnarginibus validioribus instructa, latere 

 postico vix flexuoso ; lunula linea impressa circumcincta. 

 Alt. 8 lin., lat. 9 lin. 



Hab. Off Quelpaart, 48 fathoms. 



The valve from which the above description is taken is fresh 

 and in fine condition. It is white, spotted irregularly with pale 

 orange, and the surface is smooth and shining. 



Genus Iacra, H. & A. Adams. 



Shell ovate, thin, pellucid, closed at both sides ; valves with 

 the surface divaricately sculptured. Hinge with an oblique 

 spoon-shaped cartilage-pit and a small anterior primary tooth in 

 each valve. Lateral teeth two, stronger in right valve. 



lacra Japonica, A. Ad. 



I. testa ovata, insequilaterali, tenui, pellucida, nitida, convexa, latere 

 antico latiore rotundato, postico angustiore et subproducto ; valvis 

 utrinque concentrice striatis, medio sulcis radiantibus obliquis or- 

 natis, margine ventrali arcuato, integro ; sinu palliali magno, lato, 

 profundo. 

 Hah. Kino-0-Sima. 



Smaller, more vitreous and pellucid, and with coarser sculp- 

 ture, than /. Seychellarum, A. Ad. 



Genus Thecodonta, A. Adams. 



Testa oblonga, sequivalvis, valde inaequilateralis, concentrice sulcata, 

 latere antico breviore, postico longiore. Cardo (in valva sinistra) 

 dentibus duobus divaricatis, cum dente tbecseformi prominente inter- 

 posito, munitus ; dente antico crasso, arcuato, antice tuberculiformi ; 

 dente postico lamelliformi, tenui ; dente laterali antico nullo, postico 

 conspicuo elongate. Pallii linea simplex, valde impressa et radiatim 

 sulcata ; cicatricula musculari antica triangulari profunda, postica 

 elongato-ovata. 



In form and general character this genus seems to approach 

 the fossil genus Goodalliopsis lately proposed by MM. Raincourt 

 and Munier-Chalmas for a shell from the " Calcaire grossier " 

 of Fercourt. In that genus, however, there is simply a trian- 

 gular space between the cardinal teeth, and the teeth themselves 

 are nearly similar ; while in Thecodonta there is a cup-like fold 

 projecting into the cavity of the shell, and the primary teeth 

 are very dissimilar, the anterior being of a semilunar form, with 

 a tubercular head at the theciform process, and the posterior 

 being lamelliform and nearly parallel with the hinge-margin. 

 There is only one lateral tootb, which is situated posteriorly. I 

 have drawn up my description from left valves only, so that 

 further information is required concerning the genus, especially 



