48 Studie;s in Geology, No. 3 



Family NASSIDAE 



Genus Nassa Lamarck 



A^assa zorritensis (Nelson) 



Plath; II — Figs. I, 2. 



Argobiiccinum sorritense Nelson, Trans. Conn. Ac. Sc, vol. 2, 

 p. 196, pi. 7, figs. I, 2, 1870. 



Shell large, strongly turreted, spire high, conical ; whorls 

 about seven in number. Whorls convex ; the earlier ones 

 rounded, the later ones having a prominent keel which sets 

 off a narrow shoulder, becoming stronger and more nearly 

 level with the suture as the shell grows more mature. Sculp- 

 ture of spiral cords only on the earlier whorls ; on the later 

 whorls a series of longitudinal folds begins, growing 

 stronger and more widely spaced with the growth of the 

 shell; the folds are drawn out into strong tubercles at the 

 keel, and on the body whorl the tubercles are much larger 

 and more widely spaced, with the folds dying out below 

 them in the broad surface of the shell. The spiral cords are 

 irregular ; on the earlier whorls they are well differentiated, 

 but on later whorls they often coalesce to form low, flattened, 

 strap-like ribs. The spiral sculpture lacks prominence on the 

 body whorl. The sides of the body whorl descend vertically 

 from the keel, curving smoothly into the convex base. The 

 aperture is oval-triangular, with a slight posterior mouth 

 and a short, sharp anterior canal which is sharply reflexed. 

 The columella is plicate, unworn specimens showing a sharp 

 upper plait and a thicker one below. Outer lip lirate within, 

 the lirae extending faintly for some distance. Height, 57; 

 diameter, 35 mm. (large specimen). Average specimen, 

 height, 46.5 ; diameter, 26.5 mm. 



This large and interesting species has been rather difficult 

 to place generically, and although its reference here to Nassa 

 indicates the fact that many comparisons with types have 

 shown it to belong, probably, to that genus, the author 



