54 
Aug. F. Foerste 
said to characterize the Maury phase of the Fairmount, as exposed 
typically in Maury county, Tennessee, in southern Kentucky, along 
the Cumberland River, and in central and east-central Kentucky. 
It is difficult at times to determine whether the purposes of 
science will be served best by emphasizing the close relationship 
of different forms and by grouping them all under the same spe- 
cific name, or by emphasizing their differences to the extent of 
assigning them even to different species. The present is such a 
case. Strophom-ena maysvillensis is closely related to Strophomena 
planoconvexa. Though occurring at different horizons, locally, 
they occasionally are associated, and apparently are connected 
by intermediate forms It is unfortunate that Halhs types of 
Strophomena planoconvexa were chosen from the smaller, flatter, 
and more quadrate forms, especially if Strophomena maysvillensis, 
of much more extended vertical and horizontal range, is to be 
regarded as merely the more vigorous form of Strophomena plano- 
convexa. 
Strophomena planoconvexa, Halff 
(Plate I, Figs. 1 A, B, C, D, E, F; 2 A, B) 
The type specimens of Strophomena planoconvexa, preserved 
in the American Museum of Natural History, in New York City, 
and numbered 919-2, are labelled as coming from Cincinnati, 
Ohio. They are small individuals, the larger one about 25 mm. 
in width, and belong to a form not rare at a very limited vertical 
range at the base of the Fairmount bed. At the same horizon, 
in Kentucky, half a mile north of Crescent Springs Station, on the 
Queen and Crescent Railroad, south of Cincinnati, an individual 
was found, 39 man. wide, 28 mm. long, and 8.5 mm. in convexity. 
This species is remarkable for the slight concavity of the pedi- 
cel valve. It is evident that the valve in its earlier stages of 
growth was slightly convex, especially near the beak, and had 
attained a length of 11 to 14 mm. before reversing its curvature. 
This concavity frequently does not exceed 1 mm in specimens 
35 mm. wide. 
The brachial valve usually is only moderately convex. This 
convexity frequently does not exceed 6 mm. in specimens 33 mm. 
® New York Paleontology, vol. i, p. 114, 1847. 
