266 IOWA GEOLOGICAL SURVEY 



can Museum of Natural History. Other specimens of the head 

 with associated squamation and fin structures are the property 

 of the Cambridge Museum, one such being shown in counter- 

 part at the lower corners of Plate XIII. 



From the great wealth of material that has been laid under 

 contribution it is easy to perceive that the complete fish must 

 have been one of those elaborately ornamented Palseoniscids 

 such as are embraced within the genus Rhadinichthys, and the 

 species that most readily suggest themselves for comparison are 

 those which have been described from the Lower Carboniferous 

 of New Brunswick — R. alberti, cairnsi and modulus. The aver- 

 age size of the new form would appear to be somewhat less 

 or at least not exceeding that of R. alberti, and the ornamenta- 

 tion of similar nature, but finer and more extensive. In the 

 case of some specimens, however, allowance must be made for an 

 apparent coarseness of striation or thickening of raised ridges, 

 which is plainly due to mineral incrustation. The same agency 

 is likewise responsible for an occasional enlargement of some of 

 the internal soft parts. 



Without doubt the most remarkable feature which engages 

 attention in connection with this species is the unrivalled pres- 

 ervation of soft parts. From the nature of things a state of 

 affairs of this kind is most unusual among fossils, vertebrate or 

 invertebrate. Dawson has described for us what he regards as 

 "the crystalline lens of the eye" of Elonichthys broivni* and 

 Traquair has remarked upon the "eye spots" of Thelodus and 

 Lanarkia.f Bashford Dean, too, has recently found vestiges of 

 the membranous labyrinth in the Permian Acanthodes bronni, 

 after having previously made known the delicately preserved 

 musculature of Cladoselache from the Cleveland shale.$ An 



* Dawson, J. W., Acadian Geology. 3d edition, supplement, p. 101. Lon- 

 don, 1878. 



tTraquair, R. H., Supplementary Report on Fossil Fishes, etc. Trans. Roy. 

 Soc. Edinb. (1905), 40, pt. 4, pp. 880, 882. 



JDean, B., The Preservation of Muscle-fibres in Sharks of the Cleveland Shale. 

 Amer. Geol. (1904), 30, pp. 273-8. This article contains a critical discussion of 

 Otto Reis's views concerning the conditions of fossilization. See also by the same 

 author, Notes on Acanthodian Sharks, in Amer. Journ. Anat. (1907), 7, p. 218. 



It will be convenient to refer hereto a suggestive paper by L. Cayeux on the 

 origin of phosphatic nodules, and two others by MM. Paul Combes fils and Stan- 

 islas Meunier, all contained in Bull. Soc. Geol. France (1906), ser. 4, 5, fasc. 6. 

 Important also is Joh. Lehder's article on phosphatic concretions from the lower- 

 most Culm of Thuringia, published in Supplementary Vol. 22 (1906) of the 

 Neues Jahrbuch fur Mineralogie, pp. 48-113. 



