DEVONIAN FISHES OF IOWA 89 



For our knowledge of the trunk, caudal and two dorsal fins in 

 this species, which is the only one of the genus showing these 

 features, we are indebted to the painstaking investigation of 

 Professor Patten, who has presented the following preliminary 

 account of his observations:* 



"The trunk was very slender and covered with a soft skin 

 devoid of scales or of any other markings except those men- 

 tioned below. In spite of its delicate structure it is often only 

 moderately compressed or distorted. In the region of the 

 posterior dorsal, it may present a somewhat triangular cross- 

 section, resembling that of Cephalaspis in a corresponding re- 

 gion, but without any traces of a lateral fold or of fringing 

 processes [i. e., fulcra, or marginal scales of other authors]. 



A few small irregular plates, with the typical sculpture of the 

 buckler, are embedded in the skin along the dorsal surface, 

 immediately in front of the anterior dorsal, and numerous mi- 

 nute ones are scattered irregularly over the flanks in the same 

 region. One specimen shows indications of a lateral groove, 

 and, dorsal to it, a few oblong folds suggestive of segmentation. 



The anterior -dorsal fin is low and elongated, the posterior 

 one very high and rounded. Both fins are often preserved with 

 wonderful clearness, but show no other detail than a faint stria- 

 tion probably due to the presence of delicate subdermal rays. 



The elongated tail, with its axis slightly curved, terminates in 

 a narrow band. The dorsal margin consists of a delicate mem- 

 brane, strengthened by a row of curved rods lying close to- 

 gether and arranged with great regularity. The basal ends of 

 the rods are swollen, and one is turned a little to the left, and 

 the adjacent one, to the right of the median line. The rods ex- 

 tend on to the ventral margin of the terminal band, into the 

 ventral lobe. The latter is faintly striated like the dorsal fins. 

 Its anterior ventral margin appears to divide, as though it were 

 continued forward into the lateral folds, although no such folds 

 have been detected in the trunk region. 



There are no indications whatever, either in surface views 

 or in sections, of vertebral centra or arches, and the preservation 

 of the specimens is so perfect that there is every reason to believe 

 such structures, even if formed of cartilage only, were absent. 

 Neither have we found any indication of a notochord, although 

 one may infer from the outline of the trunk that a notochord was 

 present. It was probably surrounded by a membraneous sheath 

 of no more consistency, if as much, than that in Amphioxus." 



* Patten, W., New Facts concerning Bothriolepis. Biol. Bull. 1904, 7, p. 113, 

 et seq. 



