PALEONTOLOGY. 478 



bent upward in a Ungulate extension. Dorsal valve most rotund on the umbo, the 

 beak obtuse and incurved ; middle of the valve strongly elevated in front, forming 

 an abrupt, rounded, mesial fold, which is not strongly marked posterior to the mid- 

 dle of the length, and scarcely defined in the upper part. On the sides the shell is 

 bent downward, forming on each side of the fold a deep sulcus, outside of which the 

 shell is again inflated or elevated, giving a strongly trilobed form to the front half 

 of the valve. Surface of the shell marked only by concentric lines of growth, which 

 are mostly confined to the anterior portion, and are often very numerous and 

 crowded, giving the shell a much thickened appearance on the margin. 



The species is a well-known type of the Chester limestones of 

 Illinois and Kentucky, and is often identified with Athyris {Terebratula) 

 ambigua, of the European Carboniferous rock. The Ohio specimens are 

 equally characteristic in form with any of those from the West, and may 

 be readily distinguished by its strongly trilobate form. 



Locality. — Newtouville and Maxville, Ohio. 



Genus TEREBRATULA Llhwyd. 



Terebratula turgida. 



Plate IX, figs. 21 and 22. 

 Terebratula turgida Hall, Trans. Albany Inst. vol. iv, p. 6, extract page 6. 1856. 



Shell rather smaller than medium size, ovate in general form, the point of' 

 greatest width usually below the middle of the length, and the length nearly one- 

 third greater than the transverse diameter ; base truncate and slightly emarginate. 

 Valves moderately to highly ventricose, the ventral generally the deepest and sinu- 

 ate below the middle of the length, often deeply so; beak strong, incurved, obliquely 

 and very distinctly truncate, and perforated by a proportionally large foramen. 

 Dorsal valve highly convex, with an abruptly incurved beak, which passes within 

 the deltidial opening of the opposite valve ; front of the valve sometimes convex 

 and sometimes slightly sulcated, causing the emargination or truncation of the base. 

 Shell structure finely punctate, and the surface often ornamented by concentric 

 varies of growth. 



The specimens from Ohio are larger than those from the typical 

 locality (Spergen Hill, Ind.), usually are, but not so large as they are 

 sometimes found. They correspond closely in form and general char- 

 acters, but are not so generally sulcated on the dorsal valve. They are, 

 however, altogether too similar to afford means for specific distinction. 

 The most of the specimens which I have examined from Ohio have been 

 slightly distorted by compression and in this condition may not afford as 

 many points of difference as more perfect individuals would have done . 



Formation and Locality. — In the Maxville limestone at Maxville and 

 Newtonville, Ohio. 



