INVERTEBRATE PALAEONTOLOGY. 563 



Originally we described a shell from a locality one hundred and fifty 

 Fig. 72. miles up the Yellowstone River, under the name Tur- 



ritella convexa, which seems to resemble this very closely 

 in all of its known characters, though the specimens 

 are not in a condition to show surface-markings. These 

 specimens were supposed to have coine from marine 

 Turriteiial convexa (type), beds, and the shell was, from this fact and its general 

 The apparent truncation f onil) referred provisionally to the genus Turritella. 



of the columella and lip is . 



merely due to an accidental On subsequently receiving the species above described 



from the fresh- and brackish-water beds near the 

 mouth of Judith River, their similarity of form to the specimens from the 

 Yellowstone was noticed ; but from their associations, they were believed to 

 be different. In order to avoid making a synonym, however, in case that 

 they should be found to be the same, the specific name convexa was also 

 applied to the Judith River species, under the generic name Melanin. The 

 relations of these shells still remain undetermined, owing to the condition 

 of the specimens from the Yellowstone River, which are merely casts with 

 inner layers of the shell, showing only traces of the lines of growth. In 

 order to facilitate comparison as far as possible, the annexed cut of the latter 

 shell is added. The name convexa was given from the convex slopes of the 

 spire, and. not with reference to the volutions, which are flat. 



Locality and position. — Judith River Fresh- and Brackish- water Lignite 

 beds, at the mouth of Judith River, Montana; probably belonging to the 

 latest division of the Cretaceous. 



Goniobasis convexa, var. impressa. 



Plate 42, figs. 2, c, d. 

 Melania convexa, var. impressa, Meek and Hayden (1857), Proceed. Acad. Nat. Sci. Philad., IX, 138. 



This form differs from the typical G. convexa'm being more slender, in 

 having the lower whorls much more convex, and the suture more strongly 

 impressed between the whorls below the middle. Its lip also seems to have 

 been more sinuous above, judging from the curves of the lines of growth on 

 the convex whorls. In all other respects, it agrees so nearly with G. convexa 

 that I am inclined to regard it as merely a variety of that species; should it 

 prove distinct, however, it may be designated as G. impressa, in allusion to 

 its non-compressed volutions. 



