IS PROCEEDINGS OF TIIE ACADEMY OF 



Synopsis of American Cretaceous Brachiopoda. 

 BY W. M. GABB. 



s 



The paucity of species of this order in the cretaceous formation of North 

 America is worthy of note. Among nearly a thousand species of mollusca, 

 not a dozen, in all, have as yet been discovered and characterized. This 

 arises doubtless from the fact that the only beds of the formation, yet 

 demonstrated on this continent, belong to the higher members. The upper 

 chalk comprises all the strata east of the Mississippi, and may include all west 

 of that stream, although palseontological evidence seems to indicate the existence 

 of the lower chalk, in the strata designated as Nos. 1 and 2 of Meek and 

 Hayden's section in Nebraska, as well as part, if not all, of No. 3 of the same 

 authors. The same deposits appear to exist in Texas, and may be found 

 to cover a large extent of the yet unexplored regions of the West. Two or 

 three upper greensand fossils have been mentioned as occurring in Texas, but 

 as far as my opportunities of comparison have gone, I am satisfied that they 

 are distinct. This is the case witli the two species referred by Dr. Roemer, in 

 his " Kreidebildungen von Texas," to Pecten virgatus, Nils., and Trigoaia 

 crenulata, Lam. 



Terebkatcla, Lam. 



T. Harlani, Morton. Silliman's Journal, v. 18, pi. 3, f. 16. 



T. perovalis, M., not Sow. Jour. Acad. Nat. Sci., i. ser., v. 6, pi. 3. 



T. Camilla, M. Syn. 70. 



T. Harlani, M. Syn. 70, pi. 3, f. 1, and pi. 9, f. 8, 9. 



T. fragilis, Morton, not Schlot. Jour. Acad. Nat. Sci., v. 6, p. 75, pi. 3, f. 3, 4. 



T. Atlantica, M. Jour. Acad. Nat. Sci., i. s., v. 8, p. 214. 



T. subfragilis, d'Orb. Prod. Pal. v. 2, p. 258. 



This species appears to be rather common in New Jersey. I have seen a 

 deposit in the marl pits of Hon. Nathan Stratton, near Mullica Hill, N. J., 

 almost entirely made up of the broken shells. In other places they are 

 generally found whole. They vary very much in form. Sometimes the sides 

 are as straight as the figure given in the Journal of the Academy, 1st ser., v. 6. 

 pi. 3, f. 1 ; while other specimens are much more orbicular than the figures 

 of the form referred by Dr. Morton to T. perovalis of Sowerby, and afterwards 

 called T. Camilla. The convexity of the valves varies, although generally the 

 wider the shell, the flatter is the surface of the valves. Sometimes again, 

 they show no traces of plications, and at others they are strongly plicate. I 

 have made a careful comparison of nearly a hundred specimens of this and 

 the form called T. fragilis by Dr. Morton, and I am compelled to believe, 

 against my preconceived ideas to the contrary, that they are only wide varieties 

 of the same species. True, there is no difficulty in separating the typical forms 

 of the two, so-called, species ; but, after so disposing of two-thirds of the 

 specimens, I found some of the same size and shape as fragilis with no 

 plications, except the faint ridges of the typical form of Harlani, while others, 

 having all the other characters of T. Harlani, have plications nearly as deep 

 as Dr. Morton's type of T. fragilis. The specimens of the latter form are not 

 so common as the other. M. d'Orbigny, in Prodrome de Pal. Strat., proposes 

 the name subfragilis in place of fragilis, which was pre-occupied by Schlotheim. 

 I have never seen this species, except from New Jersey and Delaware. 



T. Waco en sis, Roem. Kreid. Tex., p. 81, pi. 6, fig. 2. 

 Appears to be common in Texas. 



T. Leone ns is, Con. Emory's Report, v. 1, p. 164, pi. 21, f. 2. 



Very closely related to Wacoensis, but appears to be longer and more narrowed 

 anteriorly. I am only acquainted with this species by means of the description 

 and figure quoted above. 



Locality. Texas. 



[Jan. 



