166 PALiEONTOLOGY OF NEW- YORK. 



Ortliis tubulostriuta ( n. b.). 



Plate XI. Fia. 1-6. 



Shell circular : valves nearly equally convex, depressed near the margin. 

 Ventral valve more prominent towards the beak, which is sharply 

 incurved over the area : area narrow, and about half as long as the 

 width of the shell. 



Surface striated. Strias somewhat tubular, prominent, fasciculate, in- 

 creasing by implantation and bifurcation, extremely curved towards 

 the margins, and presenting at somewhat regular intervals small tubular 

 pore-like openings upon the surface : radiating striae, when not worn, 

 crossed by prominent concentric striae, and, rarely, by stronger lines 

 of growth. 



Cardinal process of the dorsal valve large, and nearly filling the foramen : 

 brachial processes long, slender and diverging. Area of the muscular 

 impressions in the ventral valve not strongly defined. 



This species is readily distinguished from the preceding, and from others of similar 

 form in these strata, by the prominent fasciculate striae in which the tubular open- 

 ings are very conspicuous. It may be compared with O. neglecta of Barranoe 

 ( Silurische Brachiopoden aus Bcehmen : Naturwissenscliaftliche Abhandluiigen, 

 Tab. XI, f. 11); but the figures given by that author represent the area as very dif- 

 ferent. It is unlike any other form at present known to me in the Silurian rocks of 

 the United States. 



Fig. 1-4. Young individuals of this species. 



Fig. 5, 6. Larger individuals. The two figures on eacii side of fig. 6 are enlargements of 



strisB, one without the tubular openings, and the other showing this character. 



The righthand figure shows the cardinal and brachial processes of the dorsal 



yalye*. 



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

 group : Helderberg mountains, Albany county. 



* The letters of reference for the different flgures of this and of the following species have been lea out, 

 throagh the inadvertence of the lithographer. 



