Crabs from the Cannonball Formation (paleocene) of North Dakota

More than 50 specimens of fossil crabs collected from the Cannonball formation (Paleocene) of southern Morton and Burleigh Counties, south-central North Dakota form the basis for the first report of fossil crustaceans in North Dakota. The new genus Camarocarcinus is created for their reception with the new species C. arnesoni as the type species. A separate, single, large propodus is placed in a new species, Ranina (?) burleighensis, by the senior author. The mode of occurrence suggests a near-shore condition of the Cannonball sea in this part of North Dakota. INTRODUCTION specics in as m a n y genera were known T , , „ , , from th is general a rea ( R a t h b u n , 1935). HE r a n t y of fossil decapod c rus taceans ^ h e following decapods have previously m t h e n o r t h e r n Midcon t inen t m a k e s ^een repor ted by her from the no r the rn t h e recent discovery of over 50 specimens Midcon t inen t of well preserved fossil c rabs in the C a n n o n ball format ion of sou th-cen t ra l N o r t h ^"pj^rr^ ShaleD a k o t a the more in teres t ing. These are the Dakoticancer overana Rathbun; west side Misfirst fossil c rabs t o be found in N o r t h souri River, in Corson Co. a short distance D a k o t a , a n d prior to th is find only six south of Mobridge; and along Indian Creek, Pennington Co. Necrocarcinus pierrensis Rathbun; eastern Cor_ ^ Published by permission of the State Geoloson Co. gist of North Dakota. Homolopsis punctata Rathbun; eastern Corson * Formerly Fulbright Scholar, University of Co. New England, Armidale, New South Wales; curCallianassa cheyennensis Rathbun; both banks rently U.S. Air Force. of Missouri River between the Cheyenne EXPLANATION OF PLATE 74