280 AMERICAN JOURNAL 



DESCRIPTION OP A NEW UNIO AND FOSSIL GONIO- 



BASIS. 



BY T. A. CONRAD. 



Unio rivicolus. PI. 18, fig. 4. 



Description. — Trapezoidal ; beaks nearly terminal ; dorsal 

 and ventral margins parallel; sides flattened; umbonal slope 

 rounded, slightly raised ; posterior margin truncated or slightly 

 emarginate ; ventral margin straight or slightly emarginate, ex- 

 tremity obtuse, the lower angle situated rather below the line of 

 the base ; epidermis dark olivaceous, rough with wrinkled lines ; 

 interior purplish, with wax-colored stains in the umbo ; cardinal 

 teeth thick ; lateral teeth curved. 



Locality. — Inhabits a brook near Tampa, Florida. 



Goniobasis carterii, Conrad. PI. 18, figs. 6, 7. 



Description. — Turriculated ; whorls of the spire angular near 

 the middle ; ribs rather distant, oblique, curved, obscurely tuber- 

 culated ; whorls minutely and obsoletely striated spirally, last 

 volution prominently costate on the upper half and crossed by 

 distinct raised lines ; base with five raised conspicuous lines ; 

 epidermis polished, dark olive green. 



Locality. — Barrel Springs, Wyoming Territory. Dr. J. A. 

 Carter. Right hand figure. 



Var. Left hand figure. With three distant, prominent, re- 

 volving lines on the lower half of the whorls. 



Locality. — South Park, Colorado. James Stephenson. 



Remarks. — This species of Goniobasis is probably of tertiary 

 origin and indicates an extensive lake. There are fragments 

 of a very compressed Planorbis and fragments of a species of 

 Unio, imbedded in gray indurated clay from the same locality. 



The typical form has the epidermis beautifully perfect and 

 the shell is silicified. The other specimens consist of casts in 

 chalcedony. 



