328 RESEARCH IN CHINA. 



The generic position of this form is, unfortunately, rather uncertain. The 

 ventral valve possesses, like many of the Paleozoic terebratuloids, two long dental 

 plates. In the dorsal valve the structures shown differ distinctly from those typical 

 of the genus Dielasma. Instead of having a heart-shaped plate supported from the 

 bottom of the valve by three septa converging posteriorly, I find only a single septum 

 medianly situated, with a pair of socket plates which are not very long and are close 

 to the postero-lateral margins. This structure has been observed in several dorsal 

 valves, and if it is the true and entire representation of the original condition there 

 can be little doubt that this form can not be placed with Dielasma. On the other 

 hand, I would be in much uncertainty as to where properly to refer it. If we may 

 suppose the presence of a small hinge-plate in conjunction with this distinct septum, 

 it seems likely that the form will prove to be a Harttina. 



Locality and Horizon. Post-Pennsylvanian (?) (K'ui-chou series); near Ta- 

 ning-hien, East Ssi'-ch'uan (station 5). 



Aviculipecten ? richthofeni Girty. 



Plate 29, Figures 25, 26. 

 Aviculipecten ? richthofeni GIRTY, 1907, Proc. U. S. Nat. Mus., vol. xxxm, p. 47. 



What appears to be the left valve of this species presents the following charac- 

 ters: size small, general shape semielliptical, slightly inclined backward. Length 

 and breadth approximately equal. Hinge-line nearly as broad as the greatest width. 

 Outline somewhat retracted below the ill-defined wings, but spreading again, and 

 with the sides and front broadly rounded. 



The surface is marked by angular ribs situated at relatively wide intervals, and 

 the flat interspaces are divided by very fine radiating lira;. New ribs are introduced 

 interstitially, probably by the enlargement of one of the lirae. The whole is crossed 

 by fine, somewhat lamellose, concentric lirae. 



A shell supposed to represent the left valve has an outline similar to that of the 

 right, but of course is inclined in an apparently opposite direction. There is no 

 byssal sinus, and the broad wings are undefined. The convexity is a little lower than 

 that of the right valve and the beak is less prominent. 



The surface is without ribs or radial marking, and is in fact nearly smooth, show- 

 ing only delicate, somewhat unequal and irregular concentric lines. 



This species is represented in our collections by a number of right valves and 

 only two left valves. All the larger examples of the right valve are imperfect, so 

 that measurements can not be made, but the length indicated is certainly less than 

 1 5 mm. The large specimens, so far as can be told, do not differ, except in size, from 

 the smaller ones. 



It can not be definitely stated that the flatter and nearly smooth shell here 

 described as the right valve of the species really bore that relation, but the corre- 

 spondence in size and shape and occurrence in the same beds render this interpre- 

 tation quite probable. If so, however, it is certain that the form under consideration 

 is not an Aviculipecten, since a byssal sinus, which is well developed in that genus, 

 is here inconspicuous or absent. 



In shape and sculpture this form recalls to a certain extent some of the Russian 

 speciesoL4?'z'n</a. AviculakazanensisdeVerneuil of the Russian Permian is perhaps 

 the nearest of these, though it is still considerably different. Avicula clcgantula 

 Stuckenberg of the Gschelian is still more different. 



Locality and Horizon. Post-Pennsylvanian (?) (K'ui-chou series) ; near Ta- 

 ning-hien, East Ssi-ch'uan (station 5). 



