1 79 



Cope.] -»- '^ [Julyi;, 



in place, the former occupy irregular pockets, caverns and veins. They 

 occur as incrustations, sometimes tubular and of singvilar tenuity, as 

 well as in masses. 



The breccia caverns no doubt had their origin in the same vray. The 

 ready decomposition of the limestone has permitted them to be rapidly 

 formed and filled again. 



It is interesting to note that the only similar bone deposits occur in the 

 galena bearing Hill Limestone of Illinois. These have been described 

 by Drs. Leconte and Leidy, and their species are included in the present 

 list. 



Megalonyx jeffersokii Harlan. Fragments of teeth. Found also in 

 caves in Tennessee, Georgia and Alabama. 



Stereodectes tortus, Cope, gen. et. sp. nov. 



This animal is represented by a nearly perfect upper incisor tooth, and 

 fi-agments of numerous others. It appears to be a rodent, and the tooth 

 in question presents several points of resemblance to that of Arctomys 

 monax, from which it does not differ inuch in size. The characters 

 which determine its distinction from that genus are very important, and 

 indicate widely different affinities. The central pulp cavity is exceedingly 

 small, and the tooth for a length no doubt considerably above that of the 

 A. monax, solid, with that exception. At the distal fractured extremity 

 it is narrowly linear in the plane of compression of the tooth, while at the 

 jaroximal fracture it is round, and of perhaps a shade greater diameter. 

 The anterior face of the tooth is as usual, covered with an enamel layer 

 about as thick as that in Arctomys, which extends round the outer face, 

 covering its anterior two-fifths, and is very slightly decurved on the inner 

 plane face. Viewed from the centre of the arc which the tooth describes, 

 the shaft is seen to form a slight sigmoid. The posterior narrowed mar- 

 gin forms a still stronger sigmoid, throwing the extremities of the shaft 

 in opposite directions. I have not observed this torsion in any living 

 genus of Rodentia, except in abnormal specimens. 



The specific characters are as follows : A section of the shaft is a nearly 

 isosceles spherical triangle. Distally the inner face is more nearly plane 

 than the outer, while proximally the outer is the less oblique of the two. 

 The anterior face is convex in section, and regularly continuous to the 

 outer side. There is a slight groove below the edge of the enamel on the 

 inner side, and a few weak transverse indications across the shank. The 

 enamel is nearly smooth, under the microscope displaying weak, minute 

 striae, much as in Arctomys. The arc in profile is a perfectly regular 

 segment of a circle. The color is white, and this in a matrix where the 

 yellow color of incisors of other Rodentia is well preserved. 



Lines. 



Length of chord between outer circumference at frac- 

 tured ends 10. 



Long diameter proximal end 2.8* 



Short " " " 1.8 



I am unable to throw much light on the affinities of the animal which 



