DEVONIAN FISHES OF IOWA 205 



The arrangement of cranial plates conforms closely to the 

 pattern of typical Coccosteans. The bone substance, however, 

 is much thinner, the sutures more intimately fused, and all of 

 the plates are relatively broader. The long axis of the pineal, 

 too, is transverse instead of longitudinal, as in Dinichthys and 

 Coccosteus. The enormous width and flatness of the cranial 

 and abdominal armor indicate a more or less depressed form of 

 body, probably correlated with bottom-feeding and generally 

 sluggish habits. Certainly the degenerate character of the den- 

 tition does not permit us to look upon these creatures as very 

 formidable competitors of Dinichthys and the much more agile 

 Cladoselache. 



Interesting features are displayed by the abdominal armor. 

 The mode of articulation between the headshield and antero- 

 dorso-lateral plates is less complicated than in Dinichthys, the 

 condyle and socket of the latter form being replaced by an 

 elongated flange and groove, which probably admitted of but 

 slight movement between the parts. In the type species at least, 

 the antero- and postero-dorso-lateral plates are completely fused, 

 and are overlapped to a relatively greater extent by the dorso- 

 median than in Dinichthys. 



Nothing is known of the ventral armor of Titanichthys with 

 the exception of the postero-ventro-median, certain large thin 

 plates of lanceolate outline, and found only in the detached 

 condition, having been doubtfully so interpreted. One such, hav- 

 ing a length of 29 cm, and maximum width of 12.5 cm, is pre- 

 served in the Museum of Comparative Zoology at Cambridge, 

 and is figured in the Bulletin of that institution for 1897 (vol. 

 31, pi. 5, fig. 1). It is abruptly truncated in front, and bears 

 traces of overlap by contiguous plates, thus rendering it prob- 

 able that the ventral armor of the form to which it belonged 

 was composed of the same number of plates as in Dinichthys. 



GENERA OF DOUBTFUL FAMILY POSITION. 



Fragmentary remains of Arthrodires, differing from other 

 described species as regards superficial ornament, and some of 

 them indicating fishes of considerable size, have been described 

 from various Devonian localities in the eastern United States 

 and Canada. Most of the species are known only by detached 



