FREE INSTITUTE OF SCIENCE 



961 



TERTIARY FAUNA OF FLORIDA 



Psammosolen Cumingianus Dunker. 



PLATE 28, FIGURE 15. 



Madia Cuiningiana Dunker, P. Z. S., 1861, p. 425. 

 Tagclus lincatus Gabb, Journ. Acad. Nat. Sci. Phila., 2d Ser., viii., p. 370, pi. 47, fig. 71, 



1881. 

 Madia multilineata Dall, Trans. Wagner Inst., vol. iii., part iv., p. 938, pi. 28, fig. 15, 1898 



(p- 9 2 3, Mactra m. by typographical error). 



Pliocene clays of Costa Rica, near Port Limon, Gabb; Pliocene marls of 

 the Caloosahatchie and Shell Creek, Florida, Dall and Willcox ; recent from 

 North Carolina to Texas and south to Sao Paulo, Brazil. 



At first I supposed that the extent of the incised markings over the sur- 

 face of the shell was a constant character and, as the material then in hand 

 was very different in this respect from Gabb's figures, I named the Caloosa- 

 hatchie form inultilineatus. After more thorough study of a larger amount 

 of material I have come to the conclusion that this view is erroneous, and 

 that the differences referred to come within the range of individual variation. 

 The drawing of the anterior adductor scar in Gabb's figure is obviously 

 erroneous. This form is differentiated from Psammosolen sancta-martha, 

 the other east American recent species, by its slenderness and greater relative 

 length and size. Both species range through about the same geographical 

 area, but only the former has yet been found fossil. 



Superfamily TELLINACEA. 

 FAMILY DONACID^. 



This group is very compact and simple in its characters, though requiring 

 more close examination than has usually been given to it. I have not, so far, 

 found in any of the manuals a description of the shell characters, and espe- 

 cially the hinge, which is accurate and complete. 



In the genus Donax the hinge comprises an external ligament, short, con- 

 vex, usually amphidetic, set in a deep groove which is often bordered by a 

 rib externally. Below this is a small opisthodetic resilium, seated on a pair 

 of small, short, usually excavated nymphs. The adult teeth comprise normally 

 two cardinals, very discrepant in size in each valve; the major cardinal is 

 frequently bifid, but may be bifid or simple in different individuals of the 

 same species; there are two laterals normally on the left valve, which are 

 received by sockets in the valve opposite ; but the laterals are not always both 

 in one valve, and in some of the peripheral forms of the family one or both 



