STANTON.] OSTREIDJE. 59 



Conrad's type (lower valve) measures 17 m,n from beak to base, 15 mm 

 in breadth, and 5 mm in convexity, while the corresponding measure- 

 ments of Ostrea blackii, which is the largest variety of the species, are 

 68, 62, and 32 mm , respectively. 



The extreme varieties of the three forms included in the above 

 description differ greatly from each other, and when the intermediate 

 forms and the facts concerning their distribution were unknown it was 

 natural that they should be regarded as distinct species. Conrad's 

 types were small specimens from " east of Eed river (Canadian), New 

 Mexico, Santa Fe road," where they occur in a band of brown calca- 

 reous sandstone containing Prionocyclus macombi, sharks' teeth, etc. 

 The same dwarf form is found in a similar rock in New Mexico and 

 southern and southwestern Colorado. In Huerfano park and adjacent 

 regions of Colorado the position of this brown band, which is from two 

 to four feet thick, is at the base of the Niobrara limestone, and the pale- 

 ontological evidence shows that it is on about the same horizon at the 

 other localities. In Huerfano park the Pugnellus sandstone, which 

 immediately underlies this brown band, contains great numbers of a 

 larger Ostrea that is absolutely identical in form with some of the Texan 

 specimens of Ostrea bellaplieata, but associated with them are smaller 

 individuals with larger scars of attachment showing every gradation 

 from the bellaplicata to the lugubris form. At Rattlesnake butte, 

 Colorado, 0. lugubris was found in the brown band, while the shales 

 beneath yielded fragments showing all the characters of the large 0. 

 blacldi. The collections from Texas show the forms intermediate 

 between 0. blaekii and 0. bellaplicata, both of which came from the 

 Eagle Ford shales, the equivalent of the beds from which the Colorado 

 and New Mexican specimens were obtained. From the above facts it 

 seems to me evident that Conrad's type specimens were representatives 

 of a variety that was dwarfed by unfavorable conditions, while the 

 same species under more favorable circumstances reach the large size 

 of 0. bellaplicata and blaclcii. The examples selected for illustration 

 represent most of the varieties excepting the largest ones, figures of 

 which may be found in the Fourth Annual Report U. S. Geological 

 Survey. 



Ostrea uniformis Meek. 

 PI. in, Figs. 3 and 4. 



Ostrea (Gryphcea?) uniformis Meek, 1876, Macomb's Expl. Exped. from Santa Fe" to 

 Junct. Grand and Green rivers, p. 124, PI. 1, Figs. 2a, b, c; White, 1884, 4th 

 Ann. Kept. U. S. Geol. Sur., p. 302, PI. 48, Figs. 6 and 7. 



Original description : 



" Shell small, rather thin, trigonal-ovate or subcircular in form, not 

 oblique; under valve rather deep, subcarinate along the middle, and 

 arched beneath from the beak to the opposite margin ; beak curved 

 upward, but truncated by the area so as to rise little above the margins; 



