consider this shell as Ihe young of gibbosus, Barnes ; but 

 a very slight examination serves to show that it is very dis- 

 tinct. The young of that species is alw^ays much more 

 elongated transversely, not so thick, with the beaks much 

 undulated, and the series of small cicatrices in the cavity of 

 the beaks is parallel to the hinge margin. As respects 

 magnitude it approaches parvus, Barnes, which however 

 has the beaks undulated, is rather thin, with oblique, small 

 cardinal teeth. 



REFERENCE TO THE PLATE. 



Tiic plate shows the exterior, intorior and dorsal views of the shell. 

 PI. 41. 



IINIO CAMPTODONo 



SPECIFIC CHARACTER. 



Beaks distinct from the posterior margin ; lamelliform 

 teeth arquated at tip. 



DESCRIPTION. 



Shell moderately thin, transversely oblong-oval, a little 

 compressed, dark brownish, or blackish ; beaks with regu- 

 lar small undulations, behind the middle but remote from 

 the posterior edge, but little prominent ; ligament slope 

 somewhat compressed, with two distinct compressed lines ; 

 umbonial slope not elevated above the level of the disk 5 

 anterior margin a little prominent towards the base and 



