6o Aug. F. Foerste 



hcUula, Cyclocoelia clla, FlcctortJiis plicatcUa, and evidently is the 

 Fairmonnt horizon. 



James, in proposing the term crassa, includes specimens 

 equalling- an inch and a quarter in width, and g-ives the horizon 

 as between 300 and 400 feet above low water in the Ohio river at 

 Cincinnati. This would include the Corryville. The specimens 

 from the Fairmount bed are here regarded as typical. It should 

 be noted, however, that the specimens studied by Meek were sent 

 to him by James and Shaffer of Cincinnati and evidently were 

 selected specimens. There is no species in the Fairmount at Cin- 

 cinnati which is characterized by the presence of only two plications 

 on the fold and one on the sinus. By far the greater number of 

 specimens have four plications on the fold and three in the sinus, 

 but the two lateral plications on the fold are always less conspicu- 

 ous and situated lower, on the sides of the fold. Frequently, these 

 lateral plications are quite inconspicuous, are placed half w^ay up 

 the sides of the fold, and are matched by similar inconspicuous 

 plications half way down the sides of the sinus. Specimens with- 

 out any trace of the lateral plications (the typical forms of Meek) 

 are very rare, and can be regarded as only aberrant forms of an 

 otherwise abundant species. The hinge-line generally about equals 

 the width of the shell across the middle, but may be slightly greater 

 or less. The number of plications on each side of the fold usually 

 is 5 or 6 but may equal 7. Specimens seven-eighths of an inch in 

 width are not rare at the Fairmount horizon, but the average wddth 

 is nearer three-quarters of an inch. 



PlatystropJiia costata, Pander, is a much smaller species with 

 a low fold and shallow sinus not strongly compressed laterally, and 

 having an entirely different aspeci: viewed from the anterior side. 



Platystrophia morrowensis, James. 



rPlcte VI, figs. II A,E; I2 A,B.) 



In the James collection, in Walker ]^Iuseum at Chicago Uni- 

 versity, there are several specimens labelled as the types of Ortliis 

 niorroiicnsis. Only one of these was present at the time of origi- 

 nal description of the species, and this is sufficiently characterized 

 by its very short hinge-line, equalling about one-third of the great- 

 est width of the shell. The general outline is oval, broader than 

 long. The width is 9.7 mm. ; the length, y.y mm. ; and the 

 thickness through the valves, 5 mm. The median fold is only 



