NO. 1557. NEW CHINESE PALEOZOIC FOSSILS— GIRTY. 47 



developed, or a dorsal fold with two deep channels upon its sides, but 

 the former interpretation seeni.s to be more natural. Upon that view 

 the species under consideration would be one of the antijdicata;^ and 

 its generic position would be with Nototliyrk in preference to Hemlp- 

 tijcJuna. On one side of the specimen may be noticed an appearance 

 similar to that often observed in Dlelasmd when fracture or cleavage 

 takes place along the dental plates, but in the present case this may 

 be due to exfoliation of the thick shell. Of coui'se the presence of 

 dental plates would debar this form from Nototliyrh and Heialptychlna 

 alike. 



In its specific relations this form ditiers sufficiently from any of the 

 species whose descriptions have come into ui}- hands to make a detailed 

 comparison unnecessary. It is perhaps as near to X. inflata Waagen 

 and iVi djoidfensis Abicli as any. 



Locality and horizon — Penns3dvanian (Wu-shan limestone), near 

 Liang-ho-k'ou, East Ssi-ch\ian (Station 7). 



PELECYPODA. 



AVICULIPECTEN? RICHTHOFENI," new species. 



Description. — What appears to ))e the left valve of this species pre- 

 sents the following characters: Size small, general shape semielliptical, 

 slightl}^ 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 relativel}' wide 

 intervals. The flat interspaces are marked by very fine radiating 

 lira?. New ribs are introduced interstitially, probably by the enlarge- 

 ment of one of the lira?. The whole is crossed b}^ fine, somewhat 

 lamellose concentric lirte. 



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

 to that of the right, but of course is inclined in an apparentl}^ oppo- 

 site direction. There is no byssal sinus, and the bi'oad wings are 

 undefined. The convexity is a little lower than that of the right 

 valve, and the beak less prominent. 



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

 smooth, showing only delicate, somewhat unequal and irregular con- 

 centric lines. 



This species is represented in our collections bv 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 15 mm. The large specimens, 



«This species is named for Baron von Richthofen. 



