46 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxm. 



scribed by Waagen from India or b}^ Tschernyschew from Rus- 

 sia. In fact, closer parallels can be drawn with certain Silurian 

 forms, such as Spirifer radiatus, than with those usually found in the 

 Carboniferous. In the radiatus group, as in S. hlackwelder!^ the ven- 

 tral valve possesses dental plates, Imt while socket plates, and some- 

 times a low septum, are found in the dorsal valve of the former, that of 

 S. hlackwelderi appears to be without those structures. 



Locality and horizon. — Pennsylvanian (Wu-shan limestone); near 

 Ta-ning-hien, East Ssi'-ch'uan (Stations 1 and 2). 



NOTOTHYRIS WILLISIANA," new species. 



Description. — Shell small, subspherical. Ventral valve subovate, 

 gibbous, rapidly and rather suddenly contracting at the beak, which 

 is strongly deflected and truncated h}^ a relatively large foramen. 

 Toward the front this valve is marked by a narrow, moderatel}^ strong 

 but shallow sinus extending about half the length. There should be 

 other modifications of the mesial portion to correspond with the plica- 

 tions on the accompanying valve, but if present the}^ are obscured in 

 the typical specimen. On each side of the sinus traces of some six or 

 seven ribs are found. Only about four of these are developed as pli- 

 cations on the shell, the remainder appearing on the margin, as den- 

 ticulations. Even these four, however, are obscure, and decrease in 

 intensity in proportion to their distance from the sinus. 



The dorsal valve is subcircular in outline, highly gibbous. Beak 

 small, pointed, slightly prominent. There is a strong, deep, ill- 

 defined mesial sinus, which projects in front as a sort of linguiform 

 extension corresponding to a deep emargination of the front of the 

 opposite valve. The sinus, which dies out long before reaching the 

 hinge line, is subdivided by a strong mesial fold, extending about as 

 far from the edge as the sinus itself, and each of the two channels 

 thus formed is apparently again subdivided b}^ an obscure plication 

 limited to the marginal region. On each side of the sinus there are 

 about six plications, shown rather by denticulations at the edge of the 

 shell than by folds upon its surface. 



Internal structure unknown. Shell strongly and finely punctate. 



As only a single specimen of this form was found, it was impractica- 

 ble to mutilate it for the purpose of ascertaining its internal structures; 

 therefore the generic position of the species is somewhat conjecturaL 

 The shell structure and configuration consigned it at once to the 

 Terebratulidai, and in the character last mentioned it much more 

 closely resembles the genera Notothyris and IIemi2)ty china than the 

 plicated Diela.Km as. It is somewhat uncertai n whether this fossil should 

 be regarded as having a dorsal sinus in which a mesial rib has been 



« This species is named for Mr. Bailey Willis. 



