TANAODON, A NEW MOLLUSCAN GENUS FROM THE 

 MIDDLE DEVONIAN OF CHINA 



By Edwin Kirk, 



Of the United States Geological Survcij 



In 1915 Prof. George D, Louderback of the University of Califor- 

 nia made extensive collections of fossils in the interior of China. 

 Through the kindness of Professor Louderback I have had an oppor- 

 tunity to study the post-Cambrian and pre-Carboniferous collections 

 made at that time. Recently having occasion to study MegaJomus 

 and related genera, in connection with an allied genus from Alaska, 

 I prepared specimens of a Chinese Devonian form, whicli, while 

 referable to the Megalodontidae, proves to be distinct from any 

 genus hitherto described. The genus is here described under the 

 name Tanaodon \<\i\\ Tanaodon louderhachi., new species, as the geno- 

 type. The generic name is given in reference to the long and well- 

 developed teeth characteristic of the genus. 



TANAODON, new genus 



Tanaodon^ as represented by the individuals of tlie single species, 

 is a pelecypod of medium size. The largest individual seen has a 

 maximum length of 8 cm., a maximum height of 3.8 cm. and a 

 maximum breadth of 3.8 cm. The shell is thick. In a medium 

 sized individual the shell just posterior to the hinge plate has a thick- 

 ness of 9 mm. The line marked by the angular shoulder on the 

 exterior is the line of greatest thiclmess. From this line the shell 

 thins toward the margins but at all times is heavy. The surface is 

 marked by strong concentric growth lines. These become more 

 pronounced with age and are particularly strong on the dorsal sur- 

 face. The lunule is small and scarcely differentiated. There is a 

 poorly defined escutcheon. 



The shell is elongate subrhomboidal. The greatest dimension is in 

 the line connecting the beak with the posterior margin. The line 

 is marked by a strongly developed angular shoulder. In the type 

 species the length is fully twice the height of the shell. The hinge 



No. 2661— Proceedings U. S. National Museum, Vol. 70, Art. 12. 



19148—27 - 1 



