APPENDIX. 201 



EXPLANATION OP FIGURES. 



a. Subhemispherical variety, natural size. 



h. Depressed spheroidal ditto, ditto. 



c. View from below ditto. 



(Z. Ambulacral segment and four interambulacral plates, enlarged two 



diameters, 

 c. Apical disk, enlarged two diameters. 

 /. Spine, natural size. 

 g. Base of ditto, enlarged two diameters. 



MODIOLA IMBRICAEIA, Sow. var., fig. 2. 



This is so near some English specimens that there appears no 

 reason for distinguishing it. The rib running from the umbo to 

 the neutral margin is rather nearer to the posterior side, and the 

 shell is generally broader in proportion at the extremity remote 

 from the beaks. I consequently give a figure, but I think it 

 unnecessary to propose a new name. 



Mytilus (? Modiola) Tigkensis, sp. nov., fig. 3. 



Testa irregulariter pyriformis, conico-suhovata, concentrice plicato striata, 

 verstis umiones tumida, antice convexa, poetice plana ohliqua,margine 

 antico longe recto, tunc convexo postico fere recto, post medium con- 

 caviusculo, ventrali regulariter convexo. 



Long. 50, diam. postic. 26, crass. 27 millem. 



A few well-preserved specimens were found with the last. 

 This shell approaches M. suUmvis, Sow., but it is more rounded, 

 the posterior side not being so flat, and the umbones are more 

 obtuse. 



