37 



JMactra subtruncata, PuU. Hutch. Dorset, t 5. f. 10. S'jbtrukcata, 



Lin. Trans, viii. t. 1. f. H. Tal). 27, f. 1 



We Iiave lately received from a concliological friend a 

 very thin variety of this fpecies for a diftin6l fhell, it may 

 therefore be proper to remark that thefe fometimes occur on 

 the fliores where the other ftronger fort is plentiful, as well 

 as all the gradations in fubftance. 



t)' 



Another variety is alfo obferved which very much re- 

 fembles MaBra tnmcata in contour, being nearly equi- 

 angular, and not produced at one end as ufual ; but this is 

 known from truncata by the fine tranfyerfeyZmp. 



Shell fub-triangular, white, and nearly fmooth : umbo Minutissima, 

 prominent, Infide fmooth; margin plain; hinge ftrong : 

 primary teeth in one valve two, feparated by a cavity for 

 the reception of a fingle large tooth in the opjiofite valve. 



This fpecies is one of the mod minute of the bivalve divi- 

 fion, and might eafily be miftaken for M<-ictra triangularis 

 was it not for the margin of that iliell being crenated. It is 

 however not quite fo angulated, nor fo long in proportion 

 to its breadth, nor has it ever occurred fo large as that fhell. 

 Several of thefe were taken in a new fpecies of coralline 

 together with Pe&enfragilis. 



We 



