30 Ang. F. Focrste 



nati, and Hamilton, Ohio, and I have assumed the Fairmount as 

 the type horizon. 



The cliaracteristic features of Zygospira modest a consist in the 

 low median fold, and in the rather numerous lateral plications, all 

 of them primary. In the type specimen there are 7 of these lateral 

 plications on each side, but this number is frequently 8, and some- 

 times 9. Some of these specimens attain a length of 10 mm. 



Zygospira cincinnatiensis, Meek. 



(Plate VI, figs. i6 A, B.) 



Zygospira cincinnatiensis was described by Meek as coming 

 from an elevation of 250 feet above low water in the Ohio river, 

 at Cincinnati, Ohio. Strophouiena planoconvexa, Dahnanclla 

 (Bathycoelia) hellula, Cyclocoelia ella ( = sordida), and Plector- 

 this plicatella are listed from 300 feet above the Ohio river. Dal- 

 manella niiiltisecta is said to range upward about 200 feet above 

 low-water mark of the Ohio, and Platystrophia laticosta, probably 

 including the form here described as Platystrophia profundosidcata- 

 hopensis, is listed as coming from 250 to 300 feet above low-water 

 in the Ohio. This suggests the Mount Hope bed for the origin 

 of the type specimens of Zygospira cincinnatiensis as described by 

 Meek. Unfortunately, the type specimen figured by Meek can no 

 longer be found, and the series of specimens in the James collection 

 at Chicago University numbered 164, and there labelled as t3qDes, 

 evidently are from the upper Fairmount. In view of the fact that 

 Meek's specimens were obtained from James, and considering the 

 large size of the specimens studied and the more frequent disposi- 

 tion of the plications to bifurcate, as noted in the original descrip- 

 tion, it seems more likely that the specimens received by Meek were 

 from the type series, and therefore also from the Fairmount. At 

 the time James made his early collections, the horizons of many 

 fossils was not known with the accuracy now considered desirable. 

 The specimens from the upper Fairmount, which are here re- 

 garded as typical, are distinguished from Zygospira modesta by 

 the smaller number of primary lateral plications, usually 5 on each 

 side of the median fold. In consequence the plications appear 

 larger, more angular, and more distant from each other. The more 

 prominent median elevation on the pedicel valve is due chiefly to 

 the larger size of the individuals. The four primary plications on 



