No. 380.] DEVONIAN PTYCTODONTIDA. 557 
species of Dinichthys, is abundantly verified by the new discov- 
eries, since a more ideal connecting link between Coccosteus 
and Dinichthys could hardly be imagined. Intermediate char- 
acters are most strikingly exemplified by the cranial sutures, 
sensory canals, and form of the dorso-median plate. A more 
detailed account of its organization will be presented later. 
Our purpose now is to call attention chiefly to the facts of its 
distribution, along with the accompanying Ptyctodont remains. 
In the first place, we note that Dinichthys pustulosus, Hetera- 
canthus uddeni, and probably Ptyctodus calceolus all occur 
together in the Hamilton of Milwaukee, the State Quarry fish- 
bed of Johnson County, Iowa, and in the vicinity of Buffalo, 
Iowa, and Rock Island, Illinois. The Rock Island section has 
lately been worked up in considerable detail by J. A. Udden,} 
who distinguishes thirteen different beds. Beds Nos. 2, 3, 
and 4, of his published section, contain the assemblage of fish 
remains now under discussion, but Ptyctodus also extends 
upward into Nos. 5 and g. No. 2 corresponds to the Gyroceras 
beds of Calvin and Barris, No. 3 to the lower part of the Cedar 
Valley limestone, and No. 4 to its upper part. Professor Udden 
has traced out the subdivisions of the fish-bearing beds with 
great care, and has very kindly submitted the following table 
for publication at the writer’s request, by means of which any 
one can readily orient himself when collecting in the field. 
DESCRIPTIVE TABLE OF PART OF THE SECTION OF DEVONIAN Rocks 
XPOSED NEAR Rock IsLAND, ILLINOIS. 
f (4) A slightly argillaceous bluish limestone filled with fragments of 
Crinoid stems, locally changing into a white compact limestone, from 6 
to Io feet in thickness. Megistocrinus latus Hall a prea Sen rugosa 
Hall almost invariably occur near the base of this divis n. Transition 
to the coral-bearing beds above always abrupt and PAE 
(a) An E bluish limestone weathering to a dirty yellow. 
Thickness from 15 to perhaps over 20 feet. Principal epe are: 
Aulopora sp.; Mondthledore sp.; Streptelasma rectum Hall; Atrypa 
aspera Schloth. ; Spirifer pennatus Hall; S. asper Hall ; honit i 
lum Hall; ps sen nta demissa Conrad ; S. perplana Conrad ; Orthis 
towensis Hall; a hamiltonensis Hall; Goniatites sp.; Phacops sp.; 
C aans ae Lindahl; Déinichthys fragments. 
A. 
No. 4 (= UPPER PART OF CEDAR 
VALLEY LIMESTONE). 
1 Journ. Cincinnati Soc. Nat. Hist., vol. xix, No. 3, pp. 93-95, 1897. 
