Maryland Geolocucal Suhvey 585 



Family TEREBRATELLIDAE 

 Subfamily TROPIDOLEPTINAE 



Genus TROPIDOLEPTUS Hal! 



Teopidoleptus carinatus (Conrad) 



Plate LV, Figs. 1-5 



Strophomena carinata Conrad, 1839, N. Y. Ann. Geol. Rep., p. 64. 

 Tropidoleptus carinatus Hall, 1867, Pal. of N. Y., vol. iv, p. 407, pi. Ixil, 



figs. 2, 3. 

 Tropidoleptus carinatus Hall and Clarke, 1894, Pal. of N. Y., vol. viii, pt. ii, 



pi. Ixxxii, figs. 26-36. 



Description. — Shell concavo-convex, semielliptical in outline, liinge- 

 line .straight often equalling the width of the valves. Ventral valve con- 

 vex. Dorsal valve moderately concave, sometimes nearly flat. Cardinal 

 area narrow on both valves. Cardinal process of the dorsal valve pro- 

 jecting into the open delthyrinm of the ventral. 



Surface with simple radial plications; strong and angular in youth, 

 becoming rounded and at times duplicate with age. The median rib on 

 the ventral valve is broader than the rest and produces a carination of the 

 valve. On the interior the ventral valve has strong crenulated teeth which 

 fit into similar sockets on the dorsal valve. In the latter the cardinal 

 process is conspicuous and bilobed. The loop consists of two slender 

 processes uniting in front with a median septum rising from the bottom 

 of the valve. From these two brachial processes project at points near 

 the origin of the brachidium. Shell substance highly punctate. 



The Maryland forms of this interesting brachiopod do not differ in 

 any material respect from the usual forms occurring with profusion in 

 the shales of the Hamilton group of New York, though none have Ijeen 

 seen which attain the maximum dimensions of the latter. The shells 

 bear 12-16 simple plications on either side of a large median plication 

 on the ventral valve and median depression on the dorsal. Interiors show 

 the strong crenulated teeth of the ventral valve and the siuiilarly crenu- 

 lated sockets of the opposite valve. 



Length 13 mm.; width 15 mm. 



In the Ithaca beds of New York the species occurs with other con- 

 tinuing members of the Hamilton fauna but it is with great rarity tliat 



