1913.1 NATURAL SCIENCES OF PHILADELPHIA. 501 



NEW SPECIES OF THE GENUS MOHNIA FROM THE NORTH PACIFIC. 

 BY WILLIAM HEALEY DALL. 



In arranging for study the unequalled collection of Chrysodominse 

 of the National Museum, I found an unexpected number of species 

 of the genus Mohnia Friele, of which one or two species, including 

 the type, are found in the North Atlantic. Diagnoses of some of 

 the undescribed forms are appended. 

 Mohnia robusta "• sp. 



Shell solid, stout, of about eight whorls, the apical ones being 

 always eroded in adult shells; the upper whorls with 15-16 axial, 

 rounded, little elevated, nearly straight riblets, which become feebler 

 and finally vanish on the last whorl; suture appressed, slightly 

 constricted; other axial sculpture of rather irregular, retractively 

 arcuate incremental lines; spiral sculpture of obscurely channelled 

 grooves which become wider with age and on the penultimate whorl 

 are about 14 in number; on the last whorl they are coarser on the 

 base, but nowhere sharp or clean cut; the whole surface is covered 

 with a dark olive periostracum, under which the shell is white; 

 aperture ovate, the body erased white, the pillar gyrate but not 

 pervious, the outer lip thin, sharp ; the canal rather wide and strongly 

 recurved. The nucleus is not preserved on any of the specimens. 

 The operculum is dark horn color and forms about one whorl . Length 

 of type specimen (about five whorls) 36.5; of last whorl 25; maximum 

 diameter 15 mm. 



Bering Sea in 987 fathoms, off the Pribiloff Islands. 



Mohnia corbis n. sp. 



Shell with the apex eroded and about five rounded whorls remain- 

 ing; white, covered with an olivaceous yellow periostracum; suture 

 appressed; axial sculpture of numerous, rather irregular, prominent 

 incremental lines; spiral sculpture of, between the sutures, about 

 seven cord-like ridges, which on the last whorl become flatter and 

 strap-like; the interspaces are irregular, but usually wider; between 

 the cord at the shoulder and the suture behind there is a flattish 

 space with four or five obsolete finer spirals; contrary to custom, the 

 base of the last whorl and canal have no spiral sculpture; aperture 



