346 OAKHONItMCROUS FORMATIONS AND FAUNAS OF COLORADO. 



outliii(>d by such deep grooves that thej' appear to be depressed below the general 

 surface. This peculiarity is stronger upon the ventral valve than on the dorsal, 

 where it appears upon the lateral areas, but scarcelj^ at all over the median portion. 



There is l)ut one other species of this genus known from the Western Hemisphere, 

 the South American form, Ortlwtichia morganiana. To this mj^ species is related, 

 but I feel no doubt as to their being specifically distinct. The fold and sinus of 

 0. morganiana 1 take to be less strongly marked, and the surface, as shown by 

 specimens in my jjossession, is distinctly different. It shows a feature common to 

 many species of Orthoids, consisting of individual strise somewhat more prominent 

 than the rest, terminating abruptly and running out into a small spine, but does not 

 possess the heavy, short, depressed striae which probablj^ are to be associated with a 

 similar origin, but which form such an unusual character of my shell. 



The species described by Cox as Orthh resupinoides has much the same config- 

 uration as the Colorado form, but seems to lack the peculiarities of its surface 

 ornamentation, besides which Hall and Clarke refer Cox's species to the genus 

 SchizopJioria, so that further comparisons of course are unnecessary. 



1 know of no other species with which this is likely to be confused. 



A single small specimen from Sinbads Valley has been referred to the same 

 species as that from Glenwood Springs (though it may be merely a young example 

 of Enteletes), and it discloses characters of the area which were concealed in the 

 material from the type locality. In this example, which has a length of but 14 milli- 

 meters (the type is 26 millimeters long), the beaks of the two valves are about on a 

 level when the shell is looked at from the side. The area of the dorsal valve in this 

 position is nearly vertical; that of the ventral starts out in a nearly horizontal direc- 

 tion. The areas of both valves are small, slightly curved, and contain large, open, 

 triangular foramina. That of the ventral valve is higher and more strongly- curved 

 than is that of the dorsal. 



Locality and horizon. — Grand River region, Glenwood Springs (station 2193a). 

 Dolores River region, Sinbads Valley (station 2285); top of the Hermosa formation. 



ENTELETES Fischer de Waldheim, 1830. 

 Enteletes hbmiplioatus Hall. 



1852. Spirifer hemiplicaia. Hall, Stansbury's Exped. to Great Salt Lake, p. 409, pi. 4, figs. 3a, b. 



Carboniferous: Missouri River, near Weston. 

 1859. Spirifer hemiplicata. Meek and Hayden, Acad. Nat. Sci. Philadelphia, Proc, p. 28. 



Upper Coal Measures: Near Leavenworth, Kans. 

 1866. EJtynchonella angulata. Geinitz (non Linne), Garb, und Dyas in Nebraska, p. 37, tab. 3, figs. 1-4. 



Upper Coal Measures: Bennett's Mill and Nebraska City, Nebr. 

 1866. Synirielasmlt hemiplicata. Meek and Worthen, Geol. Surv. Illinois, Kept., vol. 2, p. 323, fig. 36; 

 p. 324, fig. 37. 



LTpper Coal Measures: 12 miles north of Vandalia, 111. ; eastern Kansas, northern Missouri, 

 western Iowa. 



