4 PEOCEEDI]!^GS OF THE NATIONAL MUSEUM vol. 70 



a gradual and almost perfect gradation between cardinals and later- 

 als in this species. The teeth are long and heavy, having a fanlike 

 arrangement which makes the anterior tooth lie snbparallel to the 

 anterior margin, while the tooth farthest removed lies parallel to the 

 laterals and the dorsal margin. There are three very long heavy 

 lateral teeth. The first has its inception near the anterior end of the 

 cardinals. The second overlaps the first, while the third, beginning 

 still nearer the posterior end of the shell does not reach as far as the 

 second. Above the group of heavy laterals is a short incipient 

 tooth showing as an obscure ridge. In its anterior half the hinge 

 plate is deeply grooved for the reception of the ligament. 



The posterior muscle scar has not been seen. The anterior muscle 

 scar lies on a platform just below the group of cardinal teeth. The 

 scar is large, measuring 8 mm. across in a specimen of average size. 

 The scar proper is somewhat depressed, being bounded on the dorsal, 

 ventral, and anterior margins by a ridge. There appears to be no 

 pedal scar. The pallia! line is probably simple. 



As noted above, this species was found in the Middle Devonian 

 of the Tung Kou District, Szechwan, China, by Professor Louder- 

 back. The type specimens are in the collections of the United States 

 National Museum. 



Gotyfes.—Q2il. No. 71070, U.S.N.M. 



EXPLANATION OF PLATE 



Tanaodon louderhacki, new species 



Figs. 1, 2. Left valve and dorsal view of an individual of medium size. 3, 

 5. Anterioi* view and left valve of a large individual. 4. Interior view of 

 left valve of another specimen, showing the hinge plate, teeth, and anterior 

 muscle scar. 



o 



