35 



variably preferve their diftinguifhing chavai;:l;ers through 

 all Rages of growth, from the fmalleft to the moft perfect, 

 but all of them polTcfs a remarkable fimilarity of llruclure 

 in their lateral teeth, the infide of which is regularly crenated. 



This is the flieil Mr. Donovan has figured for MaSlra 

 fuhtruncata, the reference therefore under that head in the 

 Addenda to Tejiacea Britamika we beg may be cancelled, as 

 we have ti'ansferred it to this. That author is certainly mif- 

 taken in refering his fliell to Trigonella fiibtnmcata of Da 

 Costa, which is without doubt our MaElrafubtruncata, Tab. 

 27, fig. I . According to the fame author this fhell has been 

 found in HampJJnre and Devonjljire, but as we have never 

 been able to difcover it in the weft of England, conclude it 

 is a rare fpecies in thofe parts. Two of our fcientific friends, 

 Mr. H. Boys and Mr. Laskey, clearly pointed out the dif- 

 tin6lion of the three Madlrce in queftion, when they favoured 

 us with fpecimens of each from the northern coaft, and de- 

 nominated this by the name prefixed. 



Shell thin, fub-tri angular, truncated, and of a cinereous Cineria. 

 colour : the umbo large and very prominent ; the beak 

 flightly turned to one fide, beneath which there is a de- 

 preflion,or fub-arcuation in its contour; the oppofite fide is 

 much comprefled laterally. The infide is pale, with a tinge 

 of blufli : the hinge refembles that of MaSlra jlultorum, but 

 the valves are conliderably deeper, and the umbo projects 

 much more beyond the margin. 



E2 For 



