BRACHIOPODA. 251 



Brachial valve moderately convex, the greatest convexity in the umbonal region. 

 Surface of the shell sloping uniformly to the lateral and broadly rounded anterior 

 margins. Beak broad and incurved a little. Surface smooth except for the fine lines of 

 growth which become-more prominent near the base of the shell. 



Pedicle valve unknown. 



Remarks — The species of Meristella present a somewhat perplexing problem be- 

 cause the variation within each species is so great, and the gradation from one to another 

 is so complete that a separation of the forms is difficult. The difficulty of separating the 

 species is increased because so few entire specimens occur, the separate valves being most 

 common, and no pedicle valve can at present be linked with the brachial valve here 

 described with any degree of certainty. 



These brachial valves bear a marked resemblance to those of Meristella bella Hall, 

 but differ in being less gibbous, and in the absence of a mesial sinus which is a feature 

 of that species, and which causes an emarginate outline of the front, not noticeable here. 



Horizon — Lower beds. 



Holotype and Paratypes No. 27489, Walker Museum. 



Family Coelospiridae 

 Genus Anoplotheca Sandb. 



Anoplotheca dichotoma (Hall) 



•Plate 66, figures 22-25 



1859. Leptocoelia dichotoma Hall, Nat. Hist. N. Y. Pal., vol. 3, p. 452, pi. 103, b, 



figs. 3a-3c. 

 1913. Anoplotheca dichotoma Schuchert, Geol. Surv., Md. Low. Dev., p. 435, pi. 73, 

 figs. 24-26. 



Description — Shell small, concavo-convex, generally ovate. The dimensions of a 

 somewhat imperfect pedicle valve are: Length 8 mm., width approximately 9 mm. The 

 brachial valve of a different individual measures 7 mm. in length and 8 mm. in width. 



Pedicle valve strongly convex, the middle elevated into a fold, from which the 

 surface slopes abruptly to the lateral margins, and less steeply to the anterior margin. 

 Greatest elevation in the umbonal region. Beak elevated above the hinge line, and 

 notably incurved. 



Brachial valve flattened at the postero-lateral margins, and near the beak depressed 

 into a narrow sinus which becomes broad and shallow near the base of the shell. 



Surface of both shells marked by radiating plications, which are imperfectly pre- 

 served. According to Hall "The surface is marked by dichotomizing plications, the 

 central one of the dorsal valve becoming tripartite, and the three lateral, which are 

 simple to their original, bifurcating and making 6 at the margin of the shell. On the 

 central valve there are two smaller plications in the centre, and a dichotomizing one 

 on each side; concentrically marked by a few imbricating lines of growth." — -Hall, 1859. 



Remarks — About half a dozen separate valves have been observed. They are smaller 

 than the New York forms, and show the surface characters only indistinctly. The ovate 

 outline, the highly convex to sub-carinate pedicle valve, and the plano-convex brachial 

 valve with broad shallow sinus, are distinct features of the species which the specimens 

 exhibit. 



Horizon — Lower beds. 



Figured specimens No. 27484, Walker Museum. 



Anoplotheca fiabellites (Conrad) 

 Plate 66, figures 26, 27 

 1841. Atrypa fiabellites Conrad, Fifth Ann. Rept. N. Y. Geol. Surv., p. 55. 

 1859. Leptocoelia fiabellites Hall, Nat. Hist. N. Y. Pal., vol. 3, p. 449, pi. 106, figs, 

 la-lf; pi. 103b, figs, la-lf, 1861. 



