Xl. CONCHYhlA—DITHyRA. 



9. medium, orbiculare, costis numerosis transversiin striatis. 



orbicular, with numerous transversely striate ribs. 



10. laevigatum, obovatum iiitidum, costis ohsolelis. 



obovate and glossy, with the ribs obscure. 



11. serratiun, ohovatum nitidum sulp/mrcinn glaberrimnm. 



obovate glossy and sulphur yellow, with the ribs 

 quite obliterated. 



42. IsOCARDIA. 



1. Cor, Isocardia. 



43. Mytilus. 



1 . ungulatus, transversiin rugosiis, subquadridenlatus. 



transversely wrinkled, with four or five teeth. 



2. edulis, Iccvis, siihquadridentatns. 



smooth, with four or five teeth. 



3. incurvatus, crassns opacus incurvulus, subbideutatus. 



thick opake and incurved, with two or three teeth. 



4. pelkicidus, diaphamis radiatiis rectus, stibbidentatus. 



transparent radiate and straight, with two or 

 three teeth. 



44. MODIOLA. 



1. Modiohis, uhloHj^a solida, untich oblique dilatata. 



oblong and solid, obliquely dilated at the anterior 



side. 



2. Gibsii, Joliaceo-barbata, foliulis hint scrrutis. 



bearded with foliations which are serrate on one side. 



