104 HAY—VERTEBRATES OF CARBONIFEROUS AGE. [March 16, 
somewhat imperfectly this species under the name Rhizodus 
guadratus. Excepting that Mr. Woodward has suggested that the 
species belongs to Sagenodus, no additional information of im- 
portance has been published since 1873. Prof. Cope, indeed, 
mentions the fact that he had in his hands a single scale belonging 
to the portion of the Lacoe collection described by him and 
collected at Mazon creek, Illinois, and which he thought might 
belong to S. guadratus. 
Dr. Newberry’s figure represents well the form of the scale and 
the system of concentric lines. The system of nutrient canals is, 
however, very inadequately shown; perhaps they were not well 
displayed in the specimen figured. In my hands are two scales 
from Mazon creek (U.S. Nat. Mus. Cat., No. 5429 from Lacoe col- 
lection, and Daniels’ No. 9) which I have no hesitation in refer- 
ring to Newberry’s S. gwadratus. These scales have the size and 
the subquadrate form which characterized the original and also the 
conspicuous concentric lines of growth. One of these (U. S. Nat. 
Mus. Cat., No. 4429), looked at casually, shows little more of the 
system of canals than appear in Newberry’s figure. The other 
specimen displays them with great conspicuousness. ‘This scale 
differs in size from that of Newberry’s figure by only a trifling 
amount ; one of its posterior angles is more rounded off; the 
attached border is also much rounded ; while the free border is 
slightly concave. 
The surface of the scale, for purposes of describing it, may be 
divided into four fields, viz.: (@) an anterior, which includes all 
anterior to a line drawn across the scale somewhat in front of the 
centre of growth and therefore occupying the anterior third of the 
scale ; (2) a posterior, which is included between lines drawn from 
the centre of growth to each of the two posterior angles of the 
scale; (c) and (d@), upper and lower fields which occupy the 
remainder of the surface. ‘The field (@) is occupied by a meshwork 
of nutrient canals, the cells of which are more or less square, very 
small near the anterior border, but growing coarser and more 
irregular near its posterior limit. The triangular field (4) is oc- 
cupied by canals which radiate from the centre of growth to the 
free border of the scale. ‘These lie close together and are con- 
nected at intervals by cross canals. The resulting cells are usually 
narrow and two to four times as long as wide. ‘The intervals 
between the radiating canals are filled with very fine striz which 
