237 



Gems DIELASMA. King. 



[Ety. : I)i, two; elaama, lamella.] 



(1859 : Proc. Dublin Univ. Bot. Zool. Assoc, Vol. I., p. 260. 1893: Pal 



N. Y., Vol. VIII., p. 293.) 



Terebratuloid shells, with frequently a median sinus in 

 both valves. A large foramen and deltidial plates are pres- 

 ent, though these latter may be obscured by the incurvature 

 of the beak. A large hinge plate, raised but little above the 

 bottom of the valve, and sometimes actually adhering to it, 

 and a relatively short brachidium, with a rather short 

 recurvature of the ascending lamella?, are characteristic 

 internal features. 



The sub-genus Cranama ( Hall), was erected to receive such 

 forms as Terebratula romingeri (Hall), in which the brachi- 

 dium is that of a Dielasma, but the hinge plate resembles 

 that of Cryptonella. 



Dielasma (Cran^na) romingeri. Hall. (Fig. 149.) 

 (Pal. N. Y., Vol. IV., p. 389, PI. LX.) 



Distinguishing Characters. — 

 Small size; ovate outline; trun- 

 cated or slightly sinuate front; 

 rounded cardinal slopes ; concentric 



Fig. 149. Dielasma romingeri. 

 Stria*, which are Often Crowded into Dorsal ventral, and profile views 



(from Hall). 



wrinkles near the front. 



Found in the Pleurodictyum beds and the Calcareous bed 

 above, on the Lake Shore, and in Avery's Ravine. 



Genus TROP1DOLEPTUS. Hall. 



[Ety. : Tropis, keel ; leptos, slender. ] 



(1857: 10th Ann. Rep't N. Y. State Cab. Nat. Hist., p. 151. 1893: Pal. 

 K Y., Vol. VIII., Pt. II., p. 302.) 



Shell concavo or plano-convex, with the hinge line much 

 extended and straight, the whole aspect of the shell being 

 " Strophomenoid " (compare Stropheodonta). In young- 

 shells the hinge line equals or exceeds in length the greatest 

 width of the shell, but in mature shells it is shorter. Pedicle 



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