SEELEY — ON FOSSIL BIVALVE SHELLS. 



49 



Types with Umbonal and Posterior Teeth: 



Panopsea . 



• 1 • V* 



Cultellus 



Margaritina . * . ^ 



Mackera . 



Hippopus 



•1-2 

 •1-2 



Tancredia 



Tridacna . 



•11-11 



. 1 . 2 5 tunule perforate. 



Castalia . 



Ensis* . . 



1-2' b ' 



Unio . . . 



Solen . . 



' 2 ' 1 8 j umbones termi- 

 • 1 • 1 5 nal. 



Cyprina • 





Types with Anterior and other hinc 



Cardita . 



l-l'l*. 

 1 • 1' • 1* 



Lucina . . 



Kellia . . 



1?. i-i' 



Corbis . . 



(i i)<-i-(i i)' 



Isocardia 





Cyelas . . 



1 : (1- 1)"- l'l 



Cardiuni . 



li-ii-ii 

 ii - ii-ii 



Cyrena . 



Tellina. . 



i • i 2 1 • • l 

 1 • l i 2 • • l ' s - 



Corbicula 



Galatea . 



1 • 2 1 ' 1 ' 



Trigona . 



Donax . . 



I; 2 1 .1 ' 



Meroe* . . 



21 



1 ' 1 



2 ' 1 S; from umbo to base 

 1 • 1 ' runs an internal rib. 



2-1' 



•2- 



1' 



• 2 • 



1 



•V 



2 



• 2 



. 2 i 



-11-V 



3-1 

 1 31 -1 



s of Teeth. 



K 2 'J r a 

 l'2'l' L; b ' 



1-2-1 

 1-21 



1 • 2 1 • 1 



; margins crenulated. 



1 • 2 



i • ; 



11-311 



1' -. 3 • V 



(iiy- s -(ii)< 



1-3- 



11-3 

 1-3 



Many of the formulae will be found unsatisfactory, no doubt ; for it 

 has not been my object either to give a synopsis of bivalve genera 

 or of generic characters, but merely to illustrate the features and 

 capabilities for distinctive purposes of some remarkable mystical 

 structures. Yet I would ask the student who takes some member 

 of one of the larger types, say Donax, Tellina, Cardium, or whatever 

 it may be, and fails to torture its hinge into agreement with the 

 formula, fairly to ask, — What a genus really is ? Unless I mistake, 

 facts are as faulty as the formulse. This, however, involves the whole 

 question of the nature and origin of genera, which will shortly be 

 treated in full elsewhere. 



* A form like this is not introduced as a genus, but merely as an illustration of re- 

 sults arrived at by adhering to the formulse rigidly. 



VOL. VII. H 



