392 PROCEEDINGS OF THE NATIONAL MUSEUM. vot. 56. 



All of the Trenton triplicate species except Platystrophia prepon- 

 derosa, new species, belong to the low-fold subgroup, which preserved 

 the low fold and convex form of the ancestral stock. Members of 

 this group persisted into the Maysville, being represented by Platys- 

 trophia juvenis, new species; Platystrophia. panciplicata; Platystro- 

 phia strigosa, new species; Platystrophia nitida, new species; Platys- 

 trophia morrowensis; Platystrophia coiTyviUensis, new species; and 

 Platystrophia sublaticosta, new species. While there were seven spe- 

 cies present, four of these were confined to the Lower Mays ville and two 

 are limited to narrow horizons in the Corryville. Platystrophia sub- 

 laticosta, new species, which ranges through the Fairmount, Corry- 

 ville, and Mount Auburn, has only a scanty representation. 



There is an increase in the number of low-fold species in the Rich- 

 mond. Some of these are so similar to the Upper Trenton members 

 of the genus as to require great care in differentiation. This is 

 especially true of Platystrophia foerstei, new species, and Platystrophia 

 precursor latiformis, new variety. The Richmond species is distin- 

 guished by its somewhat deeper sinus. Platystrophia atfenuatus, new 

 species, which occurs in the Wajnesville at Waynesville, Ohio, has 

 many characters in common with Platystrophia amoena, new species* 

 of the Middle Trenton and Platystrophia juvenis of the Lower Mays- 

 ville Group. The Richmond species usually has fewer plications on 

 the lateral slopes. Platystrophia moritura of the Upper Richmond 

 is distinguished from Platystrophia precursor augusta, new variety, of 

 the Upper Trenton, with difficulty. In all these instances the 

 Richmond species has a somewhat deeper sinus. 



The writer is not inclined to regard this similarity of form as being 

 due to reversion to primitive types. The Maysville species had 

 undergone too many changes to leave no record in the ontogeny It 

 seems to indicate a reinvasion of the region by Platystrophias from 

 an area where environmental conditions during Lower and Middle 

 Ciacinnatian time did not stimulate decided change. This recur- 

 rence agrees with Doctor Ulrich's observations on the recurrence of 

 Cathey's corals. He says: "These same corals, or, rather, their 

 scarcely distinguishable descendants, appear once more in the Rich- 

 mond series of Ohio, Indiana, and Kentucky." ^ 



While many of the Richmond members are quite like those of 

 earlier horizons, there are many whose physiognomy is entirely 

 distinct. Such species as Platystrophia annieana, Platystrophia 

 clarTcsviUensis, Platystrophia cumingsi, new species, and Platystrophia 

 acutilirata are decidedly more transverse and their brachial valves 

 are more ventricose than any of the earlier forms. They also tend 

 to have a greater number of plications on the lateral slopes. 



Extreme specialization was expressed in the low fold subgroup by 

 the long hinge line and many plications on the lateral slopes. This 



« Revision of the Paleozoic System, Bull. Geological Soc. America, vol. 22, 19n, no. 3, p. 300. 



