INVERTEBRATE PALAEONTOLOGY. 273 



believe the specific name subcylindrica bad nol been used, and consequently 

 muisI lie retained here. It rather nearly resembles Atys {Roxania) Cranchii, 

 I. each, the type of thai author's group Roxania, which Adams has proposed 

 to retain as a subgenus under Atys. 



Locality arid position. — Near the mouth of Milk River, on the Upper 

 Missouri; from the Fort Pierre group of the Upper Missouri Cretaceous 



series. 



Ha mine a minor, M. & H 



Plate 31, figs. 1, a, b. 



Bulla mi,,,,,-, Meek and Hayden (1356), Proceed. Acad. Nat. Sci. Philad., 69.— Meek (1864), Smithsonian 

 Check-List N. Am. Cret. Fossils, 16. 



Shell small, ovate, very thin, greatest breadth a little below the middle, 

 rather narrow at the upper extremity; summit a little oblique, and provided 

 with a small, central, uinbilicoid depression; aperture narrow in the middle 

 and above, arcuate, widening rather gradually on the inner side below, where 

 it is rounded; surface marked by small transverse grooves or impressed striae, 

 separated by spaces generally greater than their own breadth, but sometimes 

 less, and crossed by fine lines of growth, which are sharply elevated in the 

 grooves, so as to give the latter the appearance of being punctate. 



Length, 0.42 inch ; breadth, 0.27 inch. 



When we first characterized this species, we had only seen a very small, 

 young individual, from which it was supposed to be a very small species. 

 Since that time, other specimens have been brought in, showing that the 

 adult shell attains nearly a medium size. In its general appearance, it 

 resembles the preceding species, but differs in being proportionally wider 

 below the middle, and more narrowed toward the summit. Its aperture 

 also widens more gradually below, and the transverse grooves on its surface are 

 larger; while its lines of growth are more sharply elevated in crossing the 

 grooves. As in the preceding species, its surface-markings are epiite distinct 

 on the internal cast. Possibly it may be only a variety of the last, but I 

 have not seen specimens connecting the two forms 



This species will be seen to approach somewhat the genus Scaphander, 

 and possibly may have to take the name Scaphander minor ; though it does 

 not differ very materially from the forms of some species of Bulla and 

 Haminea. 



Locality and position. — Moreau River; from the Fox Hills group, or 

 formation No. 5, of the Upper Missouri Cretaceous series. 

 35 h 





