( 7 ) 



DIVISION V. MACTRACE,E. 



1. Lutraria. Lam. M. 



Inequilateral ; gaping 

 at the lateral extremities. 

 Fig. 14. 



GENERA. 



Hinge either with 1 Ligament interior , 

 tooth folded in two, or fixed in the cardinal hoi- 

 2 teeth, one of which lows. (1) 

 is simple, with a deltoid 

 hollow close to it : no 

 lateral teeth. 



«. Shell transversely oblong. 



^. . . orbicular or sub-trigonal. 



2. Mactra. Gmel. M. 



Inequilateral, subtrigo- 

 nal ; a little gaping at the 

 sides : beaks protuberant. 

 Fig. 15. 



3. Crassatella. Lam. M. 



Inequilateral, suborbi- 

 cular, valves close. Fig. 16. 



4. Unculina. Baud. 



Shell transverse, round- 

 ed above, almost equilate- 

 ral : valves close, fur- 

 rowed. Fig, 19. 



5. Erycina. Lam. M. 



Sub-inequilateral , equi- 

 valved, rarely gaping. 

 Fig. 20. 



1 compressed cardi- Ligament interior, in- 

 nal tooth, folded in a serted in the cardinal 

 furrow on each valve, hollow. (2) 

 with a hollow close to it ; 

 or 2 lateral compressed 

 teeth. 



2 sub-diverging car- Ligament interior, in- 



dinal teeth, with a hoi- serted in the hollow of 



low at the side : lateral each valve. (3) . 

 teeth none, or obscure. 



A short sub-bifid car- 

 dinal tooth on each 

 valve, with an oblong 

 marginal hollow by its 

 side, divided in two by 

 a contraction. 



2 unequal cardinal 

 teeth, diverging, with 

 an intervening hollow : 

 2 lateral oblong teeth, 

 compressed, short. 



Ligament interior, in- 

 serted in the hollows 

 and seen without. (4) 



Ligament interior, 

 fixed in the hollows. {5j 



(1) This shell is sometimes found in the sand at the moutli9 of the rivers of 

 France. Foss. in the Mart Pits of Toumine. 



(2) Frss. in Great Outitc, Crag Marl, at Grignon. 



(3) The greater number of species become very thick with age. Atlantic, 

 Coast of Guinea, East and West-Indies, New-Holland, Southern Seas. Foss at 

 Grignon,Bourdcaux, St.Bricux,Couriagnon, Magnitot> Vauclusc, Beauvais Jioudan. 



(4) There is only one species ; habitat unknown. 



(5) The only living species known, comes from New-Holland* Foss. &tHoudan f 

 Parries^ Pontchartrain, Grignon, Ecouen. 



