50 THE NAUTILUS. 



The following modification of the key may be made: 



a. Aperture strongly 3-dentate or 4-dentate. 



b. Basal tooth simple, tubercular or somewhat elongate; 



diam. 12-13 mm. A. thomsoniana. 



b\ Basal tooth distinctly bifid ; diam. 14- 16^ mm.; umbilicus 

 wider. A. thomsoniana porterte. 



a 1 . Aperture toothless or without teeth on the outer lip, etc., etc. 



To those who do not have access to Ancey's original description, 

 it may be useful to have his note on the supposed variety orobcena. 

 He says: "Very closely allied to the preceding [tltomsoniana~\, 

 being similar in the number of whorls and size, but differing in hav- 

 ing the last whorl scarcely descending at its termination, higher, the 

 aperture larger and less oblique." 



These characters seem to be merely individual rather than racial. 

 It is from the same locality as A. tJioitisoniinia. Besides the speci- 

 mens of thomsoniana in the Academy received from the late Mr. J. 

 H. Thomson, of New Bedford, Mass., part of the original lot, we 

 have received A. thomsoniana from Mr. Ashmun, who lias lately col- 

 lected a few specimens in Santa Fe Canon, the original locality. 

 The species differs widely from Pulygyra krettei, which is not an 

 Ashmunella but apparently a true Pulyyyra. 



NEW SOUTHERN UNIOS. 



BY BERLIN II. \VK1GHT. 



U. dispalans, sp. nov. 



Shell uniformly thin, oblong-elliptical, flattened, inc<|iiilatfral, 

 smooth, with close slightly elevated growlh ridges; anterior margin 

 abruptly and uniformly rounded, base very slightly rounded, anterior 

 abruptly pointed, dorsal margin straight; epidermis yellowish and 

 nearly occulted by the light green fasciculated rays ; beaks small 

 and surrounded by Jour or five irregular undulating ridges; umbonal 

 slope uniformly rounded or subangular ; beak cavities slight; cica- 

 trices smooth, slightly impressed and showing the successive nacreous 

 layers, anterior ones distinct, posterior ones indistinguishable ; dorsal 

 notch very long and shallow, ligament long, depressed, thin ; cardinal 

 teeth low, very oblique, thin and obliquely striated, lateral teeth 



slender, long, nearly straight, double in the left and single in right 



t 



