184 REPORT UNITED STATES GEOLOGICAL SURVEY. 



24. Mactra (Cymbopftora) icarrenana Meek & Hay den. 



This speeies was found in the upper strata of the Fox Hills Group, both 

 at the month of the Saint Vrains and near Aaron Eaton's farm in the 

 valley of the Cache a la Pondre ; also, at Fossil Ridge, the strata of 

 which are near the base of the group. The examples from both the lat- 

 ter and the first-named localities are referred to this species without 

 hesitation, but those of the second-named locality appear to agree more 

 nearly with the description of M. (O.)formosa Meek & Hay den. How- 

 ever, I regard the difference between these two forms as varietal only. 

 The range of the species is through the whole of the Fox Hills Group as 

 developed in Colorado east of the Rocky Mountains, but it seems never 

 to have been found in the Fort Pierre division in the Upper Missouri 

 River region. 



25. Plioladomya? 



A single fragment, evidently belonging to this genus, was found at the 

 mouth of the Saint Vrains. It is plainly different from P. subventricosa 

 Meek & Hay den, which has been found only in strata holding a similar 

 stratigraphical position at the mouth of Judith River. It is probably 

 new, but the specimen is too imperfect for characterization. 



26. Glycimeris berthoudi White. 



This fine species has been found only at Fossil Ridge, in strata near 

 the base of the Fox Hills Group. It is figured and described in another 

 part of this volume. 



27. Pacliymya f lierseyi White. 



This species is figured and described in another part of this volume. 

 It was found by myself only in the upper part of the Fox Hills Group as 

 developed in this district, and only at the mouth of the Saint Vrains 

 and in the valley of the Cache a la Poudre; but Mr. A. Lakes has 

 obtained it from a similarly high horizon in the valley of Bear Creek, 

 near Morrison, Colo. It is figured and described in another part of this 

 volume. 



28. Teredo f 



In a tragment of fossil wood obtained among the other fossils at Little 

 Thompson Creek I detected borings, evidently of Teredo, or an allied 

 form, but they were too imperfect for specific determination. 



29. Dentalium gracile Hall & Meek. 



Our examples were found in considerable numbers in the uppermost 

 strata of the Fox Hills Group at the mouth of the Saint Vrains and in 

 the valley of the Cache a la Poudre. They were found only in the form 

 of casts, which, not showing the surface characters very clearly, leave a 

 little doubt whether they may not really belong to another species, but 

 they seem to be identical with D. gracile. The type specimens were 

 obtained from the upper beds of the Fort Pierre Group in the Upper 

 Missouri River region. 



30. Cylichna scitula Meek & Hayden. 



The type-specimens of this species were obtained from the Fox Hills 

 Group on the Moreau River, a tributary of the Upper Missouri. It 

 seems not to be a common species, as it has not been reported from any 

 other locality until it was found in the district here discussed. I found 

 it only in the uppermost strata of the Fox Hills Group, and only at the 

 mouth of the Saint Vrains and in the valley of the Cache a la Poudre. 



