2 PEOCEEDINGS OF THE NATIONAL MUSEUM vol. 73 



the surface of the ridge as well as the space anterior to it is granu- 

 late. Front with a sharp well advanced median tooth with a small 

 tooth on either side; outline obscure but the accessory tooth points 

 obliquely outward. Orbital slits deep and open, the inner sinus longer 

 than the outer, its outer margin exceeding the inner margin, while the 

 reverse is true of the outer sinus ; margin between the sinuses oblique 

 and nearly straight. Outer orbital tooth broad, tipped by a long, but 

 thick and slightly curved spine, convex outside. The antero-lateral 

 spine of the carapace is similar to the orbital spine but longer ; it also 

 is curved but directed very slightly outward, but not so far as the line 

 of the widest part of the carapace. The postero-lateral margin is 

 slightly sinuous and marked by a raised line formed by a single row 

 of close granules; it rounds into the truncate posterior margin. 

 Length of carapace 12.6, width 8 mm. The above description is 

 made from a small specimen imbedded in a cross section in such a 

 way that only the dorsal surface of the carapace is exposed. Cat. 

 No. 369608, U.S.N.M. 



Fortunately another specimen showing sternal as well as dorsal 

 surface was taken previously from the Midway, basal Eocene, near 

 Kerens, Navarro County ; it was submitted to Dr. W. L. Stephenson 

 by D. W. Ohern, Borealis Oil Co., Oklahoma City. This specimen 

 lacks the frontal and orbital regions ; it measures 25.6 mm. in length 

 up to the anterior base of the lateral spine; approximate width 22 

 mm., estimated length 34.6 mm. Carapace (pi. 1, fig 1) very convex 

 from side to side, high in the middle where it forms a broad smooth 

 ridge ; either side of it on the posterior half of the carapace there is 

 a shallow depression; at the widest part of the carapace on the left 

 side (the right side is broken away) there is a large round smooth 

 boss. I am not sure that this is natural to the crab as it looks much 

 like a swelling due to parasitism. 



Additional occurrence. — Two specimens were taken in the Midway 

 of southwestern Arkansas at Buzzard Bluff, sec. 16, T. 14 S., R 26 

 W., Miller County, by J. P. D. Hull, and were returned to him. 



GoTuparison with type-species. — So far as the carapace and sternum 

 '(pi. 1, fig. 2) are concerned this species agrees in all essentials with 

 the Recent or type-species of the genus. The postero-lateral margins 

 ^converge more rapidly and the posterior margin is correspondingly 

 shorter than in N. chimmonis. The lobe at the middle of the supra- 

 orbital margin is subquadrate instead of triangular. 



