2 PEOCEEDINGS OF THE JTATIOXAL MUSEUM vol. v-i 



is there a marked change in the growth lines as they cross it. The 

 band is situated above the middle of the whorl. Its lower edge 

 marks the periphery of the whorl, and the band itself lies at an angle 

 on the sloping upper surface of the whorl. The band is flat to 

 slightly convex. As shown by the growth lines, the slit band on the 

 free margin lay at the apex of a deep, sharply angular V-shaped 

 notch. The upper surface of the flange or carina has its inception 

 somewhat below tlie middle of the whorl and at the base of the 

 flattened lateral zone below the band. Its lower surface seems to 

 be along the line of contact between adjacent whorls. The flange is 

 thick in its inner portion, becoming thinner toward the margin. The 

 flange lies in contact with the upper surface of the infrajacent whorl 

 and in part seems to have coalesced with it. It is only by careful 

 chipping away of this portion of the flange that the upper surface 

 of the whorl can be seen. The flange does not drop down over the 

 slit band but flares abruptly outward at its upper margin. 



BatJmiopterus may readily be distinguished from Euomphalopterus 

 by its wide umbilicus, its deep apertural notch and slit band, and the 

 very different character of its marginal flange. There seems to be 

 no other genus with which Bathmopfeims may readily be confused, so 

 long as the shell is preserved. 



In the Guelph of Ontario are gastropods commonly referred 

 to EuoinphaJ,opteims. Such material as I have seen is in a very 

 poor state of preservation and can not well be determined with 

 certainty. I think, however, that the Guelph material is not refer- 

 able to Euomphalopterus, and if not referable to Bathmopterus, as 

 seems equally probable, represents a new genus. 



Type. — Bathmopterus li^ratus, new species, is the type and only 

 known species of the genus. So far as known the genus is restricted 

 to the upper Silurian of Alaska. 



BATHMOPTERUS LIRATUS, new species 



Plate 1, Figs. 1-5 



This species is founded on one excellent specimen and several 

 fragmentary specimens. All the essential structural characters are 

 well shown by the material available for study. 



The spire is low, the sides diverging at an angle of about 105°. 

 Measurements give a height of 3 centimeters and a maximum 

 breadth, exclusive of the flange, of 5.5 centimeters. The whorls are 

 closely appressed. In the apical portion of the shell the whorls over- 

 lap the preceding whorls to about one-half their height. The fifth 

 whorl is overlapf)cd b}- the sixth to not more than one-sixth its 

 height. In the intermediate zone there is a progressive change from 



