A NEW SPECIES OF CERITHIOPSIS FROM ALASKA. 



By Paul Bartsch, 



Assistant Curator, Division of Mollusks, U. S. National Museum. 



Among a lot of shells recently received for determination from ]\Irs. 

 Kate Stephens, of San Diego, California, collected by her in Alaska, 

 are several new forms of Pyramidellids and a C'eritliioysis. 



The Pyramidellids have been described in the monograph upon this 

 family now going through the press and the Cerithio'psis is character- 

 ized below. All the types were kindly donated to the U. S. National 

 Museum. 



CERITHIOPSIS STEPHENSI, new species. 



Shell elongate conic, chocolate brown. (Nuclear whorls decollated 

 in all the specimens seen.) Post-nuclear whorls well rounded, orna- 

 mented spirally by four keels between the sutures, of which the 

 posterior three are strong and tuberculate, the fourth smooth and 

 slender. Axially the whorls are marked by irregular ribs, 

 the junctions of which with the spiral keels form tuber- 

 cles. The posterior row of tubercles is at the summit 

 and is the weakest, the individuals appearing as rounded 

 knobs. The second is on the middle of the whorl. This 

 and the first, which is immediately above the peripheral 

 sulcus, have their tubercles of about equal strength. On 

 these two keels the tubercles slope gently anteriorly and 

 very abruptly posteriorly. The peripheral sulcus and 

 the other two sulci are equally strong and wide. All 

 are crossed by the ribs, which, however, do not extend 

 over the base. Both spiral cords and ribs are crossed 

 by strong incremental lines. Sutures constricted. Pe- 

 riphery of the last whorl marked by a deep channel. 

 Base well rounded, rather short, marked by strong incre- 

 mental lines and a few very fine spiral striations. The 

 summit of the succeeding whorl drops a little below the peripheral 

 sulcus in all the whorls of the spire and allows a narrow margin of the 

 smooth base to appear as a cord in the suture. Aperture ovate, with 

 a strong anterior sinus, outer lip thin, showing the external sculpture 



Cekithiopsis 

 stephensi. 



Proceedings U. S. National Museum, Vol. 37— No. 1711. 



399 



