BATHMOPTERUS. A NEW FOSSIL GASTEROPOD GENUS 

 FROM THE SILFRIAN OF ALASKA 



By Edwix Kirk 

 Of the United States Geological Survey 



In a rocont paper published in these Proceedings^ I briefly dis- 

 cussed an upper Silurian horizon that is widely distributed in Alaska. 

 In the present paper is described a new gastero[)od genus from 

 this horizon. 



BATHMOPTERUS, new genus 



This genus superficially resembles Euomphaloptei-us. This resem- 

 blance is due to the general form of the shell and the possession 

 of a broad marginal flange. Here the resemblance ceases, however. 

 Bathmoptei^s has a Avell defined though nontypical slit band and 

 is apparently referable to the Pleurotomaridae, or possibly the 

 Euomphalidae, rather than the Rhaphistomidae. 



The genus is Euomphaloid in general appearance. The spire is 

 low and broadly spreading. Six closely appressed whorls are present 

 in the figured specimen. The umbilicus is very large and open. The 

 upper surface of the whorl is convex. Laterally the whorls are flat- 

 tened, giving way again to a gently convex area on the under side 

 of the whorl which marks the zone of contact with the succeeding 

 Avhorl. The inner portion of the whorl is convex and drops off 

 rather abruptly from the contact zone. 



The growth lines on the upper surface of the whorls are directed 

 backward to the slit band. Below the band the growth lines are 

 sharply flexed backward in the vicinity of the band. The lines are 

 then carried outward on the broad flange or carina, where from a 

 backward attitude they curve gradually until in the marginal area 

 of the flange they are at right angles, or even directed slightly for- 

 ward. The growth lines on the under surface of the flange parallel 

 those of the upper surface. The slit band is no more than a flattened 

 area in which the growth lines abruptly change their direction. So 

 far as seen, the band is not sharply delimited by marginal ridges, nor 



' Proceedings United States National Museum No. 2692, vol. 71, art. 20, pp. 1-9, 1927. 



No. 2763.-PROCEEDINGS U. S. NATIONAL MUSEUM. VOL. 74 ART 18 

 6641—28 



