196 PALEONTOLOGY OF NEW JERSEY. 



This shell has been variously referred to Ostrea, Gri/phcea, and Exogyra 

 by different authors, but its general characters do not correspond with the 

 generally accepted features of any of these forms. In Vol. I, p. 15, Ameri- 

 can Journal of Conchology, Mr. Conrad proposes for a similar Eocene spe- 

 cies the generic name Grypliccostrea, and in the Report of the U. S. Geolog- 

 ical Survey of the Territories, p. 11, Mr. Meek offers a generic diagnosis fur- 

 nished by Mr. Conrad, and mentions this species as a typical form on Mr. C.'s 

 authority. He also mentions in a foot-note that on well-preserved speci- 

 mens of this species he has seen long, slender, auricular appendages on each 

 side of the hinge. I have not seen these appendages, to my positive knowl- 

 edge, except on the anterior side, although they are not uncommon on the an- 

 terior side of the lower valve. I think the generic separation of the group 

 of which this may be considered a typical form a necessary one, as it has a 

 decidedly spiral or twisted beak, but without the hinge features of Exogyra. 

 This might be said to be an evidence that Exogyra and Gryphcea ought to be 

 included under one generic division, as this is an intermediate form, which 

 may be quite true, but where there are groups of species having such dis- 

 tinctive characters as this possesses, convenience demands some considera- 

 tion ; whereas many generic divisions are recognized in cases where it is ex- 

 tremely difficult to point out specific differences. The species has been re- 

 ferred to Ostrea lateralis, Neils., by several authors. I have not been able 

 to examine specimen of that species, but from the figures which I have 

 seen I should be led to doubt their identity. Oysters, however, are so 

 variable that if one takes the extremes of any of the species from a given 

 locality they would be likely to pass beyond the typical form of one or 

 more other species, so that if we were to follow it out we should soon have 

 but one species in all. 



Formation and locality. — The species is very abundant in the Middle 

 Marl Beds, at Timber Creek, and near New Egypt, associated with Tere- 

 bratula Harlani. It also occurs as casts at Mullica Hill, and at localities in 

 Monmouth County, New Jersey, in beds which I suppose to be in the 

 Lower Green Marls. 



