48 COLORADO FORMATION AND ITS INVERTEBRATE FAUNA, [bull. 106. 



temporaneous, it may be well to enumerate some of its most character- 

 istic forms. Those given in the following list are not known to range 

 into strata above theOolorado formation and all are sufficiently abundant 

 and widespread to be of use in correlation. Many others are equally 

 as characteristic, but have been found at only one or two localities: 



Ostrea lugubris. ■ Cardiuin pauperculum. 



Exogyra columbella, Liopistha (Psilomya) meoki. 



Gryplisea newberryi. Liopistha (Psilomya) concentrica. 



Avicula gastrodes. Turritella wkitei. 



Gervillia^propleura. Glauconia coalvillensis. 



Inoceraraus labiatus. Pugnellus fusiformis. 



I. dimidius. Baculites gracilis. 



I. fragilis. Buchiceras swallovi. 



I. umbonatus. Scaphites warreni. 



I. exogyroides, Prionocyclus. 



I. deformis. Prionotropis. 



I. undabundus. Mortohiceras. 



• 

 Kone of the keeled Ammonites included in the last three genera 



above named have been found above the limits of the Colorado forma- 

 tion audits equivalents in America. 



The fauna is also negatively characterized by the absence of many 

 types that form prominent features of the Mon tana fauna. Among such 

 maybe mentioned the genera Heteroceras, Ptychoccras, and Anjsomyon, 

 the large species of Baculites, such as B. ovatus, grundis, and com- 

 pressus, Scaphites conradi and Scaphites nodosus, and the broad com- 

 pressed forms of Inoceramus, like I. sagensis and I. vanuxemi. 



The Eagle ford shales and the Austin limestone of Texas have already 

 been alluded to as the equivalents of the Fort Benton and Niobrara, 

 respectively. This correlation was made on a good paleontological 

 basis by Shumard, Meek,' White, and others, and it has never been ques- 

 tioned. The faunal lists published by Mr. 11. T. Hill 1 contain the fol- 

 lowing species that occur in the Colorado formation or are represented 

 by closely related forms : 



From the Eagle Ford shales. 



Ostrea congesta. Buchiceras swallovi. 



0. bellaplicata [lugubris.] Mortoiiiceras shoshonense. 

 Exogyra columbella. Prionotropis woolgarL 

 Inoceramus exogyroides. Ancyloceras? annulatus. 



1. involutus [umbonatus.] Ammonites graysonensis. 3 

 I. labiatus. Ammonites meekianus. 3 



From the Austin limestone. 



Ostrea congesta. I. labiatus. 



Exogyra columbella. Trigonarea sp. 



E. lajviuscula. Nautilus elegans. 



E. ponderosa. Mortoiiiceras vespertinum 



Inoceramus exogyroides. (=Amm. texanus). 



I. involutus. Mortoniceras shoshonense. 



I. umbonatus. Baculites asper. 



1 Geol. Sur. Tex. Bull. No. 4, Check List, Cret. Invert. Foss. of Tex., pp. 51-53. 



2 These probably are species of Prionotropis. 



