INVERTEBRATE PALAEONTOLOGY. 303 



PECTINIBRANCHIATA. 



TRITONIDjE. 



Genus TRACHYTRITON, Meek 



Si/nou. — Buccinum (sp.), Hall and Meek ; not Liniiaus. 



Trachytrilon, Meek (1804), Smithsonian Check-List X. Am. Cret. Fossils, 22 and 37— Gabb (18C9), 

 Pakeout. Cal., 11,154 (as a subgenus under Tritonium). — Schmidt (1873), Petref. der 

 Kreidi'. von der Insel Sachalin, 17 (as a genus). 



Etym. — rpo^tj, rough; Triton. 



Type.— Buccinum vinculum, Hall and Meek. 



Shell fusiform or subfusiform, with spire shorter than the combined 

 lengths of the aperture and canal : volutions convex, rounded, or angular, hist 

 one more or less enlarged, and contracting into a somewhat produced, nearly 

 straight, or moderately bent canal below; surface witli vertical folds, or 

 costse, and revolving lines or little ridges ; inner lip typically well developed 

 all the way up, but not much thickened; columella without plaits or folds ; 

 outer lip thin, excepting at irregular intervals, where it became thickened 

 and denticulate within, so as to form distinct internal varices, which were 

 not subsequently absorbed, but left behind as the shell advanced in growth, 

 thus producing strongly-defined, pitted furrows, on casts of the interior. 



The most marked feature of this type, is, the internal thickening and 

 denticulation of the outer lip at irregular intervals, so as -to form internal 

 varices that leave their impressions strongly defined on casts of the interior. 

 The external folds, or costse, of the type-species are quite well defined and 

 regular on the upper volutions, but become less distinct and more irregular 

 on the body-volution. Generally, there are some irregularities or interrup- 

 tions of the marks of growth at the points where the internal varices occur; 

 but no well-marked external varices, distinct from the vertical folds, exist. 



The California species referred by Mr. Gabb to this genus have the 

 body-volution somewhat more ventricose than in our type, and, in one instance, 

 angular around the middle; while, in the other, the vertical folds are mainly 

 confined to the most convex part of the body-volution, and show a slight tend- 

 ency to assume the character of mere elongated nodes. In one of the Rus- 

 sian species referred to it by Schmidt, this character is even more decidedly 

 marked: the folds on the volutions of the spire being merely represented 

 by a row of nodes around the middle of each turn. In all of these species, 

 however, the revolving external ridges, or little bands, as well as the charac- 



