462 CRETACEOUS PALEONTOLOGY. 



interspaces, and occupying the greater portion of the shell, the 

 more anterior of these ribs are shorter and curve strongly for- 

 ward, the more posterior ones curve slightly downward ; between 

 these strong ribs and the curved divisional furrow is a subtri- 

 angular area occupied by much smaller somewhat nodose fur- 

 rows, which usually have a more or less distinct upward curva- 

 ture as they approach the posterior border. The upper portion 

 of the valves is divided into two regions, being nearly in the 

 plane of the valve below and abruptly inflected above to the 

 hinge-line, to form a long and rather broad escutcheon, this 

 region is marked with 12 or 14 subangular ribs which originate 

 along the divisional furrow, curving backward and upward 

 across the escutcheon to the hinge-line. The entire surface is 

 also marked by more or less irregular concentric lines of growth. 



Remarks. This is one of the most abundant species in the 

 Marshalltown clay-marl near Swedesboro, where it occurs with 

 the shell perfectly preserved. Morton's original illustration of 

 the species from Alabama is very imperfect, but the Swedesboro 

 specimens do not differ in any essential respect from the speci- 

 mens illustrated by Conrad and Gabb from Eufaula, Alabama. 

 Whitfield's species T. mortoni, described from internal casts and 

 a single very imperfect external impression, is doubtless iden- 

 tical with this Swedesboro and southern species. 



Formation and locality. Marshalltown clay-marl, near 

 Swedesboro (177); Wenonah sand, near Crawfords Corner 

 (i26 3 ); Navesink marl, Atlantic Highlands (108), Freehold, 

 Holmdel (Whitfield). 



Geographic distribution. New Jersey, Alabama, Mississippi, 

 Arkansas, Texas. 



Trigonia eufaulensis Gabb. 



Plate XLVIII., Figs. 5-10. 



1860. Trigonia Bufalensis Gabb, Jour. Acad. Nat. Sci. Phil., 



2nd ser., vol. 4, p. 396, pi. 68, fig. 32. 



1861. Trigonia Bufalensis Gabb, Synop. Moll. Cret. Form., p. 



232 (176). 



1864. Trigonia Bufalensis Meek, Check List Inv. Foss. N. A., 

 Cret. and Jur., p. 9. 



