FREE INSTITUTE OF SCIENCE 



581 



TERTIARY FAUNA OF FLORIDA 



It is observable that the ascent of the hgament and the obsolescence of 

 the resilium has taken place in shells of all types ; so that, in the subfamily 

 Mallednce, related most nearly to the Ledals by the porcellanous constitution 

 of the shell, we have Lediform, Yoldiform, and even Nuculiform types. It is 

 also notable that the external ligament is sometimes amphidetic, and in some 

 other cases, when functionally opisthodetic, is so supplemented by a continua- 

 tion forward of the periostracum as to appear amphidetic. In Malletia proper 

 there is a tendency for the edge of the hinge-plate to turn up so as to form an 

 anterior lateral tooth of a feeble kind which corresponds to a groove in the 

 hinge-plate of the opposite valve, while in Plenrodon (or Niiculind) the anterior 

 lateral is fully formed and conspicuous. In several forms in which there is no 

 internal resilium in any stages yet observed, there is a vacant triangular area 

 between the anterior and posterior ranks of teeth which corresponds to the 

 area occupied by the chondrophore in Leda and Yoldia, and which, if not 

 observed with great care, might easily be mistaken in a fossil for a functional 

 chondrophore. 



Subfamily MALLETIN^. 



The groups included in this subfamily are as follows : 



Genus MALLETIA Desmoulius, 1832. 



(+ Solciiclla Sby., 1832, + Ctcnoconcha Gray, 1840.) 



Type M. Norrisii (Sby.) = chilcnsis Desm. 



Shell yoldiform, with external opisthodetic Hgament amphidetically ex- 

 tended by periostracum and resilium, but neither lunule nor escutcheon, the 

 anterior tooth row short and the rostrum obsolete. Psetidoinalletia Fischer is 

 synonymous, ^^^ Verrill. 



Subgenus? NEILO A. Adams, 1852. 



Type N. aitstralis Quoy and Gaim. (-|- N. Cimniigii Ads.). 



Shell like Portiandia, the anterior and posterior teeth more nearly equal 

 in number. 



N. gigantea Smith from Kerguelen is intermediate between this group 

 and Malletia proper, both in amount of rostration and number of hinge-teeth. 

 M. obtusa Sars, the type of Pseiidomalletia, has absolutely no trace of rostrum, 

 though, according to Sars, it has at least one long siphonal tube. 



Genus TINDARIA Bellardi, 1875. 

 Type T. arata Bellardi ; Pliocene of Italy. 



