190 PALEONTOLOGY OF CALIFORNIA. 



T. Gibboniana, Lea? 



PI. 17, Fig. 178, and PI. 31, Fig. 262. 



[T. G ibboniana, Lea. Trans. American Philosophical Soc, 1840, p. 255, pi. 0, 

 fig. 7.) 



(T. Hondaana, Lea. Id., p. 256, pi. 9, fig. 9.) 



(T. Hondaana, D'Orb. Prodrome, vol. 2, p. 106, Etage 17, No. 711.) 



Shell rounded, subquadrate, compressed; beaks anterior, sub- 

 terminal ; cardinal and basal margins nearly parallel, the former 

 nearly straight, the latter broadly convex; anterior end broadly 

 rounded, straight near the beaks ; posterior end truncated ob- 

 liquely above, vertically below. 



Surface in adult specimens marked by about thirteen nodose 

 ribs, starting from a line drawn from the beaks to the posterior 

 basal angle, and running obliquely downwards and forwards; 

 those nearest the beaks becoming more oblique and somewhat 

 curved ; above are some smaller pustular ribs, or rows of small 

 tubercles, running parallel with the corresponding posterior 

 margin of the shell. In very young specimens all of the ribs 

 are reduced to rows of distinct tubercles, and those on the car- 

 dinal border change their direction somewhat. Besides these, 

 on two specimens from Martinez, is a single row of small, 

 isolated tubercles, placed between the two rows of ribs. 



Figures, natural size. 



Localities: Near Martinez, and Jacksonville, Oregon. 



D'Orbigny, in his Prodrome de Paleontologie Stratigraphique, refers T. Hon- 

 daana to the Neocomien. Our specimens are undoubtedly from the equivalent 

 of the lower part of the Upper or White Chalk of Europe, the Senonien of D'Or- 

 bigny. Should I be correct in my reference of this shell to Lea's species, it will 

 prove either an unusually wide stratigraphical range for the species, or some 

 mistake on the part of the French author. Be that as it may, I can find no valid 

 characters, in the poor figures and meagre description given by Mr. Lea, by 

 which I can separate his species from the present one. It is also possible, 

 although there is no present means of deciding, that his T. Tocaimana may be 

 the same as T. Evansii; and that Naiica Gibboniana, figured on the same plate, 

 may be Amauropsia alveata, Naiica id., Con. 



