ISO |Sekate 



has generally Been referred to S. Icsvicosta, Lk. sp. {Terelratulites ostio- 

 latus, ScHLOT.), from -which, it differs in l)eing less gibbous, and having a 

 depressed line aloEg tbe mesial elevation of the dorsal valve. It may be 

 easily distiaguished from S. eurutines of Owen, with which it is associated, 

 by its narrower and much more arcuate area and less angular plications. 

 Some specimens show renaains of a faint impressed line along the centre 

 of each plication. 



Geological position and locality. Limestone of the age of the Uppey 

 Helderbeirg : Falls of the Ohio, and vieinity. 



Spisifer yaricostjs (n.s.). 



Pal. N.Y. Vol.iv. 



Shell siibsemicircular, lengtli less than half the width ; hinge 

 equalling the greatest breadth of the shell, and terminating in 

 salient angles : dorsal valve marked on each side of the narrow 

 somewhat prominent mesial fold by about ten elevated, simple, 

 angular plications ; mesial elevation abruptly elevated at the 

 sides, flattened or slightly depressed along the middle ; beak 

 projecting little beyond the hinge, and, together Avith the narrow 

 area, slightly incurved : ventral valve much the more convex^ 

 most prominent at the umbo, having ten or twelve plications on 

 each side of the sinus, in the centre of which is sometimes a 

 faint indication of a single plication ; sinus distinctly defined to 

 the apex of the beak, which is pointed and slightly arched • 

 area somewhat high and extending to the extremities of the 

 hinge, slightly arcuate; foramen narrow triangular. Surface 

 marked by regular distinct imbricating lines of growth, which 

 sometimes give a subnodose character to the plications. 

 This species differs from S. eurutines of Owen, in being smaller and 

 more transverse, with more angular plications and stronger concentric lines 

 of growth ; also in the greater prominence of the two plications bounding 

 the dorsal sinus of the present species, as well as the abrupt and angular 

 mesial fold. 



Geological position and locality. Limestone of the age of the Upper 

 Helderberg : Falls of the Ohio, and Charleston landing, Indiana. 



