LOWER HELDERBERG ROCKS 91S 



Trematospira globosa ( n. s). 



Plate XXXVI. ¥io. 1 a - p. 

 fValdheimia ghbosa : Descr. of New Species of Pal. Fossils, in Regents' Report for 1856, p. 47. 



Shell subglobose or ovoid. Ventral valve a little larger and slightly less 

 gibbous than the opposite one, most gibbous in the umbonial region : 

 beak prominent, rounded and arched, perforate at the extremity by a 

 round aperture, the lower side of which is formed by a deltidium. 

 Dorsal valve shorter than the ventral, very gibbous in the middle : 

 beak incurved. 



Surface marked by twelve to sixteen somewhat angular plications on 

 each valve, two or three of which are slightly depressed on the middle 

 so as to produce, sometimes, a faint emargination in front ; the de- 

 pressed plications smaller than the others, and often becoming obso- 

 lete before reaching the beak. A few strong concentric imbricating 

 lines of growth cross the plications : shell granulose. 

 The globose form and elevated subangular plications of this shell, as well as the 



generally more distinctly imbricating lamellse, giving it a rude form, will serve to 



distinguish it from the following species of the same rock. 



Fig. 1 a - e. Dorsal, profile, and front views of young individuals. 



Vig.lf-k. Individuals of larger size. 



Fig. 1 I - p. Individuals of full size, showing some differences in the plications, and in the 

 elevation of the beak. 



Geological position and locality. In the shaly limestone of the Lower Helderberg 



group : Helderberg mountains, Albany county. 



Trematospira formosa ( n. s.). 



Plate XXXVI. Fig. 2 a - t. 

 fFaldheimia formosa : Descr. of New Species of Pal.'Fossils in Regents' Report for 1856, p. 48. 



Shell longitudinally ovate. Ventral valve tapering towards the beak : 

 beak prominent, rounded, arched or incurved, truncated at the apex 

 by a round perforation, one side of which is formed by the deltidium. 

 Dorsal valve gibbous, sometimes most prominent near the umbo : beak 

 closely incurved beneath the opposite one. 



