288 THE AMERICAN MIDLAND NATURALIST 



Genus GRACILERECTUS. N. Gen. 



Fossil sea plants or seaweeds, attaining a small to medium size; 

 stems simple, succulent, cylindrical or sometimes compressed; 

 broadly or sharply curved, but sometimes straight; generally 

 distantly branched, branches sometimes opposite; surface smooth 

 or at times irregular ; terminations sharp to rounded ; root of medium 

 size, flattened or subcircular, generally constricted above, surface 

 smooth or marked by elongated elevations. 



Gracilerectus Hackberryensis. N. Sp. 



Stem of this seaweed simple, surface nearly even, cylindrical 

 or sometimes compressed, surface smooth so far as known; broadly 

 curved; distantly branched, branches sometimes opposite. Ter- 

 minations round to pointed. Diameter 1-4 to 3-4 inch; length 

 apparently six inches to two feet or more. 



This fossil, in its usual aspect, presents the appearance of nu- 

 merous linea stems, often extending half a foot to two feet or more 

 in length, and always appears in the form of casts. 



Position and locality: Often crowding the strata of the lower 

 portion of the Lower Hackberry Group (the lower part of Fenton's 

 "Cerrogordo Sub-stage"; at Mason City, Iowa, and other points. 

 So far as known this species is restricted to the Hackberry Group. 



Now in the author's collection. 



Genus FRUTICRISTATUM. N. Gen. 



Stems of this seaweed rounded, not known to attain a greater 

 diameter than one fourth inch or slightly more, stems terminated 

 by a tuft of long, rounded succulent branches equal in diameter 

 to the main stem, and these branches sometimes bifurcate; surface 

 of main stem smooth, usually straight but sometimes bent. 



Fruticristatum iowense. N. vSp. 



Stems of this remarkable seaweed or "fucoid," round, three- 

 sixteenths to one-fourth inch or slightly more in diameter, three 

 and a half to four or more inches in length. Stem terminated by a 

 tuft of long, rounded succulent branches equal in diameter to the 

 main stem. These branches sometimes bifurcate. Main stem 

 smooth, usually straight but sometimes bent. 



The large slab of limestone before me and whose upper face is 



