iSo 



most closely resembles certain genera of the family Rhynchospiridac. The 

 only distinction is that the shell is impunctate in the new genus, and this leads 

 the writer to place it in the family Athyridac. If the new Chinese forms 

 are to be classified under Athyridae, the definition of the latter family must 

 suffer a slight but important change. I<"or it is said thai in Athyridae, the 

 shells are smooth, lamellose, or spinose, but not radiated by ribs^' ; while 

 there are many coarse radial ribs in the new Chinese genus. 



As to the jugum, however, nothing is accessible to the writer, and con- 

 sequently it is not clear to which of the two subfamilies this genus should be 

 united. It appears, however, that he ma\' be led to established a new, or 

 third, subfamil}' of Athyridae, distinguished from the others by possessing 

 radial ribs on the surface of the shell. This can only be decided by further 

 comparative studies of similar groups of fossils. 



Genotype : — At]iyrisi)ia squciiiiosa nov. gen. et sp. 



Beside this type species there are two other forms that belong to the 

 genus, one being a variety of the genotype, and the other being an indepen- 

 dent species. They are 



Athyrhina sqiiauiosa var. rhoiiiboidalc nov. 



Athyrisiua minor nov. 



Geological Age : — Middle Devonian. As to the determination of the 

 geological age of the present genus, readers are requested to refer to the fol- 

 lowing pages on which the individual forms are explicated. 



Athyrisina squamosa nov. sp. 



PI. XXIII., Fig. 5,6, 1 6 and 17. 



Outline slighly transverse, biconve.x, the ventral valve being higher than 

 the other. Hinge-line short and somewhat curved ; and about half of the 

 maximum breadth of the shell. Ventral valve has a distinct median sinus, 

 which begins at the tip of the beak and extends from the front margin in the 

 form of a tongue. The beak is not very acutely pointed and terminates in a 



i) See Eastman's Text-book of Paleontology, vol. J., p. 417. 1913. 



