374 Certain Shells in the British Museum, 



C. Front and hinder Slope grooved. 



14. Spisula solida ; Mactra solida Montague. 



15. Spisula crdssa ; Mactra crassa Turton. 



16. Spisula subtruncata ; Mactra subtruncata Montague. 



17. Spisula triangularis ; Mactra triangularis Lam., E. M., t. 253. f. 3. 



IV. Lutra v ria Lam. Lutri'cola Blainv. 



Shell oblong, longitudinal, rounded, and gaping at each end. Cardinal 

 teeth two in each valve ; the anterior ones of the left valve trigonal, nicked 

 beneath ; the hinder ones often wanting. Lateral teeth small ; the anterior 

 one simple, short, nearly perpendicular close to the hinge teeth, often 

 wanting in the right valve ; the hinder one oblique, very thin, rudimentary, 

 often absorbed as the shell enlarges in growth. Siphonal inflection very 

 deep, ovate. Animal like Mactra. Siphons united, large. 



At first sight, one might consider L. hyans as forming a distinct genus ; 

 but the young have as distinct lateral teeth as any of the other species ; 

 but this tooth, and the space that it occupied, is absorbed into the carti- 

 lagic pit as the shell grows. 



A. Shell ovate, rather gaping behind. 



1. Lutraria elliptica Lamk. {fig. 32.), Sow. Gen.; Mactra Lutraria Linn., 

 Lister, C. t. 415. f. 259. ; Chemn., C. vi. f. 240, 241. 



Inhabits sandy coast of Europe ; Fossil, Italy. 



2. Lutraria senegalensis n. s. Shell narrower. 



Inhabits coast of Africa. 



See, also, Lutraria elliptica var. b. Lamk., and L. ensis Quoy Voy. 

 Astrol. t. 83. f. 36. 



3. Lutraria plandta ; Mactra planata Chemn., vi. f. 238, 239. Hinder la- 

 teral teeth very distinct, simple in each valve. 



a. Shell slightly gaping behind, with a distinct Lozenge, edged with a raised Line. 

 Hinder lateral Teeth wanting in the Adults. 



4. Lutraria elongdta n. s. Shell elongate, ovato-lanceolate, solid, white, 

 tapering behind, oblique. 



Inhabits Prince of Wales's Island. 



5. Lutraria compressa Lamk., No. 4. ; Lfgula compressa Leach, Bacosta, 

 t. 13. f. 1.; Encyc. Method., t. 257. f. 4., Lister Conch., t. 253. f. 88., 

 Ang., t. 4. f. 23. ; Mactra piperita Gmel., Chemn., vi. f. 21.; Lutricola 

 compressa Blm. t Man., t. 77. f. 2.; Cannula Adanson Seneg., t. 17. 

 f. 18. 



Inhabits North Sea, Africa, Senegal, Mediterranean. 



* Shell widely gaping behind. Lozenge without any posterior Ridge. Lateral 



Teeth distinct. 



6. Lutraria solenmdes Lamk., No. 1., Sow. Gen., f. 1. ; Mya oblonga Gmel., 

 Chemn., vi. f. 12. ; Mactra hyans Dillwyn ; Lutricola solenoides Blan. 



