46o CRETACEOUS PALEONTOLOGY. 



In the South where the two species, costata and ponderosa 

 occur, they have the same stratigraphic relations as in New Jer- 

 sey, that is the ponderosa occurs in lower beds than the costata. 



Formation and locality. — Marshalltown clay-marl, near 

 Swedesboro (177). 



Geographic distribution. — New Jersey, Alabama, Texas. 



Exogyra sp. 



Plate XLVII., Fig. 3- 



In the Merchantville clay-marl the internal casts of a small 

 Hxogyra sometimes occur which cannot be certainly referred to 

 either B costata or B. ponderosa. They are always small, rarely 

 attaining a width greater than 28 mm. Their external charac- 

 ters have not been observed. 



Formation and locality. — Merchantville clay-marl, Lenola 

 (163). 



Geographic distribution. — New Jersey. 



Super-family TRIGONIACEA. 

 Family TBIGONIIDAE. 



Genus Trigonia Bruguiere. 



In certain of the faunas of the New Jersey Cretaceous, the 

 genus Trigonia is abundantly represented, in others it is nearly 

 or quite absent. Unfortunately, however, the specimens are 

 nearly always represented by internal casts and impressions of 

 the exiterior, which latter are not always so preserved as to 

 admit of being used for moulds tO' secure artificial casts. Four 

 species are recognized in the present report, but several others 

 are suggested among the recent collections of the Survey, but 

 are too incomplete to allow of their proper description. 



Trigonia tlioracica Morton. 



Plate XL VIII., Pigs. 1-4. 



1834. Trigonia thoracica Mort., Synop. Org. Rem. Cret, Gr. 



U. S., p. 65, pi. 15, fig. 13. 

 1852. Trigonia thoracica Roem., Kreid. von Texas, p. 52. 



