214 IOWA GEOLOGICAL SURVEY 



Some years ago the writer had occasion to examine New- 

 berry's types of Chemung Ctenodipterines, and became con- 

 vinced that the five species of Dipterus proper made known by 

 that author from Pennsylvania were in reality manifestations 

 of but two tolerably distinct types, the one represented by D. 

 nelsoni, the other by D. flab elli for mis. The so-called D. levis of 

 Newberry was shown to have been founded upon worn speci- 

 mens of D. nelsoni, and the small teeth described as D. minutus 

 and D. quadratus were regarded as probably immature exam- 

 ples of the same species. This latter interpretation was held to 

 be substantiated by close intergradations between the smaller 

 forms and the altogether similar but larger teeth of the pre- 

 vailing type. More recently the writer has been, fortunate in 

 having at his command an excellent assortment of Dipterine re- 

 mains from the Chemung of Pennsylvania, collected by Mr. F. 

 A. Randall, and a review of this material has suggested a still 

 further reduction in the number of species. In the light of well 

 preserved specimens which reveal the complete characters of the 

 dentition, it is impossible to doubt that the thin, flat, usually 

 more or less crushed and broken plates known as D. flabelli- 

 formis are the palatine components of the same dental appara- 

 tus whose mandibular elements have received the name of D. 

 nelsoni. The five species that have been recognized from the 

 eastern Chemung rocks thus become resolved into one,* and it 

 is probable that the detached scales, ceratohyal bones, and labial 

 cartilage (the latter known as Ganorhynchus beecheri) which 

 accompany the teeth of D. nelsoni belong likewise to one and the 

 same species. 



Now it is of interest to recall that a species corresponding in 

 some respects rather closely to D. nelsoni occurs in the Upper 

 Devonian of Iowa, and like its eastern associate, is of protean 

 habit. That is to say, it assumes a multitudinous variety of 

 shapes, due to age, wear, and various sorts of mechanical and 

 even chemical deformation after death. In addition, there are 

 the usual distinctions of outline and surface contour which, after 

 analogy with D. nelsoni and D. flab elli formis, are to be under- 



*Or at least not more than two, in case the small teeth of the D. minutus type 

 are regarded as constituting a distinct species, instead of being the young of D. 

 nelsoni. The only conspicuous difference is that of size. 



