DEVONIAN FISHES OF IOWA 149 



rate, others not. Dorsally are seen two longitudinal fossae which 

 mark the position of the neural arches. The texture is every- 

 where quite compact, that of the intervertehral faces being espe- 

 cially dense, yet exhibiting under the lens the structure of calci- 

 fied cartilage. 



3. TUBERCULATED DERMAL PLATES. 



Different varieties of detached tubercles, some of them of 

 large size, and other dermal ossifications evidently of Elasmo- 

 branch (and possibly Holocephalic) nature are found in consid- 

 erable abundance in the Kinderhook limestone near Burlington, 

 LeG-rand, and elsewhere in Iowa. Some of these tuberculated 

 plates and spiniform bodies bear a strong resemblance to those 

 found in natural association with Myriacanthus, as figured by 

 Smith Woodward (Cat. Foss. Fishes Brit. Mus. pt. 2, pi. 3, fig. 

 4, and Quart. Journ. Geol. Soc. 1906, 62, pi. 1, figs. 4, 5), and on 

 that account may be provisionally referred to Palaeozoic Chim- 

 aeroids, — that is to say, Ptyctodontidae. That members of this 

 family were in existence as late as the dawn of the Carboniferous 

 is proved by the occurrence of Ptyctodus eastmani in the Grlen 

 Park limestone (Kinderhook) of Jefferson county, Missouri, and 

 by the presence of an undescribed species of Ehynchodus in the 

 Waverly of Boyle county, Kentucky. These Lower Carbonif- 

 erous forms are to be regarded, however, as archaic survivals of 

 late Upper Devonian fish faunas. 



An idea of the general appearance of the tuberculated dermal 

 plates occurring in the Iowa Kinderhook, and tentatively re- 

 garded as of Chimaeroid nature, may be had from an inspection 

 of the illustrations given in Plate II, Figs. 12 and 15, the orig- 

 inals of which are preserved in the Museum of Comparative Zool- 

 ogy. In the same category should be placed the curious spini- 

 form bodies described under the name of Erismacanthus bar- 

 batus, and the small falcate spines called Physonemus pandatus 

 and P. hamus-piscatorius* Dean and others have suggested 

 with much plausibility that the defenses known as Cyrtacanthus 

 dentatus, from the Ohio Corniferous, and the Lower Carbonifer- 



*BulI. Museum Comp. Zool. 1903, 39, no. 7. 



