PLATE LXXVII. 



(Figures 1-ii, •2:i-'>a li.v K. 1!. 1\Ii:i:k ; 1", 11, 17-3-2 by G. B. SijipsoN ; li-U liy K. r. \V ii rn- 1 i;li> ; 20-28 by F. J.SWINTON.) 



Subgenus BEACHIA, s.-gen. nov. 



Page 2iiu. 



Beaciiia Suessana, Hall. 



Fii;: 1. Tlie interiors of two iiedlcle-valves, the upper retaining- the deltidial plates, the lower having- 

 lost tho?e 1 lutes, but sliowing- the dental lamellie. Both tig-ures show an obscure musculai' 

 area divided by a low median ridg-e. 

 Vig. 2. The interior of a biacUial "\alve -, showiiifT the hing^e-iilate. nicdi.-iUy de|>i'essed and pei-forated at 

 its a|iex liy tli(; visceral for.-inien, the dental sockets, and the form of the loop with the meilian 

 roil-like process extending- backward and npwai-d fi-om tlie anterior plate. 



. Front view of conjoined valves ; showing the fine plication of the surface and the inflexion of the 

 lateral margins, 



. Median lony-itiidinal section of conjoined valves; showing in profile the loop with its long, erect 

 (•rural apopliy.ses, the elevation and direction of the median proi-i>ss extending backward from 

 the anterior plate. 



. Views of the interior of two brachial valves ; showing the inflei-ted lateral margins and some vari- 

 ation in the comlition of the hing-e- plate. 

 7, 9 Ventral, pi-ofile and dorsal views of a typical example ; showing the outline, contour and 

 plication of the valves and their lateral marginal inflexion. 



. Profile of a smaller shel'. with tlie mai-ginal infiexion of the valves extending to the anterior ex- 

 tremity. 



, 11. Views of the liing-e-]ilate in two individuals ; showing difterences due to age ami consequent 

 thickening of the parts. X '2. 



Oriskany sanilstone. Owmherlanrl. Maryland. 



(iENis MEGALANTERIS, Suess. 



P.age ill. 



Megalanteuls ovalis. Hall. 



Fig. 12. An internal cast of the pedicle-v.alve ; show-ing the filling of the deep scar of the diductor muscles, 

 enclo.sing the small sub(;ordate addui-.toi- .scar, with traces of vascular sinu.ses and genital 

 markings. 



Fig. 13. The dorsal side of an internal cast; showing the deep impression of the prominent hinge-plate 

 and cardinal process, and the ailductor muscular scars. 



Fig. 14. A similar view of another .specimen to which a portion of the pedicle-valve adheres i showing the 

 cavity of the hinge-plate and the <livision of the muscular area into anterior and posterior 

 scars. 



Oriskany .sandstone. St-lwharie, JVew York. 



Fig. 15. The ventral side of another internal cast ; showing the impressions of the muscular scars and vas- 

 cular sinuses. 



Fig. 16. Dorsal view of the same specimen; sh'-wing the deep cavities left by the grooved cardinal pro- 

 cess, crural bases, and adductor scars. 



Figs, n, 18. Posterior and interior views of tlie cardinal portion of the brai-hial valve, enlarged ; showing 

 the hinge-plate and the stout, erect, bilobed and deeply grooved cardinal process, the broad 

 crural bases, and a porti(m of the muscular impression. X 2. 



Figs. 19, 20, 21. Interior, profile and front views of a gutta-percha imjire-ssion taken from a natural cast of 

 the interior, having a vei-y highly developed cardinal process divided on its posterior face by 

 a single median groove ; showing also the crural bjises and muscular area divided by a low 

 median septum. 



Fi"-. 22. The umbonal j^ortion of the brachial valve, drawn/rom a gxitta-percha impression taken from the 

 specimen represented in tig. 16 The two grooves on the posterior face of the c:irdinal process 

 are charactei-ized by series of tine, diverging lines. 



Oriskany sandstone. Albany county. New York. 



