PROC. BIOL. SOC. WASH. 101(1), 1988, pp. 72-78 A NEW CRAB, SEORSUS WADEI, FROM THE LATE CRETACEOUS COON CREEK FORMATION, UNION COUNTY, MISSISSIPPI Gale A. Bishop Abstract. —A fossil dakoticancroid crab, Seorsus wadei, new genus and species, is described from the early Maastrichtian Coon Creek Formation of Union County, Mississippi. This crab belongs to the Dakoticancer Assemblage pre-viously described from the Blue Springs locality. The only known specimens consist of a nearly complete, crushed, carapace steinkem and a partial carapace steinkem. Seorsus differs from other members of the Dakoticancridae in car-apace proportions, shape and ornamentation. Collection of the Blue Springs locality (Bishop 1983) on 10 Mar 1984, resulted in the discovery of a new fossil crab. The Blue Springs locality is situated geographically in the Mississippi Embayment, an ancient arm of the Cretaceous Tethys Seaway that oc-cupied much of present Mississippi, Ala-bama, and western Tennessee. Two speci-mens were collected from the sandy clay stone shelf sediments of the Coon Creek Formation of early Maastrichtian Age (Rus-sell et al. 1 983). Correlation with other North American Cretaceous rocks indicates an ab-solute age of approximately 67 million years before present. Both specimens are internal casts of the carapace and are preserved as steinkerns. Systematic Paleontology Order Decapoda Latreille, 1 803 Superfamily Dakoticancroidea Rathbun, 1917 Family Dakoticancridae Rathbun, 1917 Seorsus, new genus Type species.— T\iQ type species of 5*^0^-sus is Seorsus wadei, n. sp. Diagnosis.— C3.r2i^SiCQ of moderate size, longer than wide (L/W = 1.10), widest at anterior Vs; lateral margins distinctively convergent posteriorly; grooves broad, moderately defined; areolations very tumid, especially epibranchial lobes; cardiac region with small central tubercle; metabranchial region with subtle transverse and submar-ginal ridges. Claws and legs unknown. Etymology.— ^^^Qorsus" is derived from the Latin; apart, separate, severed, to in-dicate the carapace shape which sets this taxon apart from the other dakoticancroid genera and also the fragmented or severed nature of both specimens. The gender is masculine. Occurrence.— Seorsus is known from a single species based on two carapace spec-imens from the Coon Creek Formation, ear-ly Maastrichtian, of Union County, Missis-sippi. Seorsus wadei, new species Fig. lA-F Diagnosis.— CaraipdiCQ longer than wide (L/W = 1.10), widest at anterior Vy, lateral margins distinctively convergent posterior-ly. Grooves and areolations similar to those in other members of family. Carapace evenly granulate. Description. —Carapace 1.10 times longer (23.3 mm) than wide (21.1 mm), widest at anterior Vs; front relatively straight; antero-lateral margin broadly rounded; lateral mar-gins relatively straight, converging poste-
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