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TERTIARY FAUNA OF FLORIDA ' 



Between species like M. siibstriafa, in which the hinge of both valves is 

 fully developed, and those in which the cardinal hook or lamina is obsolete, 

 or the differentiated left lamina is represented only by a bevelled inflection of 

 the cardinal margin, there is really only a difference of degree, and a differ- 

 ence which may perhaps be of only specific value, and even I am inclined to 

 suspect sometimes exhibited by individuals within the species. After a careful 

 study of all the material at my command, recent and fossil, I find the follow- 

 ing species among others should be referred to Montacuta as restricted : M. 

 substriata Mtg., M. Vbriugi Friele (N. Atlantic), M. ferriiginosa Mtg., M. 

 ftoridana Dall (West Florida), M. (Decipula) ovata Jeffreys (not Montacuta 

 ovata Jeffreys, which is a Rochefortia), and M. chipolana Dall, of the Oligocene. 

 All the species referred by Verrill and Bush ("Revision of Deep-water Mol- 

 lusks," Part i., 1898) to Montacuta will under the present arrangement be re- 

 ferred to Rochefortia. 



Montacuta claiborniana n. sp. 

 Plate 45, Figure 21. 



Eocene sands of Claiborne, Alabama ; Burns. 



Shell small, thin, polished, smooth, nearly equilateral, very slightly arcuate, 

 moderately inflated ; beaks low, dorsal margin thin, evenly arcuate, passing 

 distally into the rounded ends, of which the anterior is shorter and less high; 

 base slightly arcuated ; in the left valve the posterior dorsal margin above the 

 scar of the internal ligament is somewhat reflected, the single minute cardinal 

 is under the beak with a slight fold extending forward. Lon. 1.7, alt. 1.2, 

 diam. i.o mm. 



A single small valve was obtained from Claiborne shell sand. Though 

 doubtless immature, it is described as being the only representative of the 

 genus in this horizon, M. Dalli Cossmann being, under the present arrange- 

 ment, 'referred to 5or;H'a. 



? Montacuta chipolana n. sp. 

 Plate 44, Figure 4. 



Oligocene of the Chipola beds of Calhoun County, Florida, on the Chipola 

 River, and in the lower bed at Alum Bluff ; Dall and Burns. 



Shell small, very inequilateral, the posterior side very short, dorsal and 

 ventral margins nearly parallel, straight, passing evenly into the bluntly rounded 

 ends ; the young have the posterior end proportionately less short and the 



