650 GEOLOGICAL SURVEY OF IOWA. 



CORALS AND BRYOZOA. 



THE Corals of this formation are of the cyathophylloid 

 character, among which the one figured is the most charac- 

 teristic. The Bryozoa are chiefly of the Fenestellidse ; 

 among which, the spiral forms, or the Archimedes of LESUEUR, 

 are very conspicuous. The species here illustrated, in its en- 

 tire structure and characteristics, is the most common form, 

 and will serve to give a correct idea of this group of species, 

 which, so far as we know, begin their existence in the Keo- 

 kuk limestone, and continue at least as far as the Kaskaskia 

 limestone, and perhaps to the limestones of the Coal mea- 

 sures. 



Zaphrentis spinulifera ( n. s.). 



PLATE XXII. FIG. 1 a, b. 



CORAL in the form of an elongated reversed cone, curved. 

 Calyx slightly oblique, circular or subcircular, the cavity 

 deep ; septal fosset strongly marked, situated on the inner 

 side of the curvature. Radiating lamella strongly defined, 

 somewhat irregularly curved, numbering at the margin from 

 forty-two to fifty, and uniting in fascicles of two, three, four 

 or more before reaching the centre : outer wall of the calyx 

 thin at the upper margins, becoming very thick and strong 

 below. Externally somewhat rugose, and often swelling ab- 

 ruptly at intervals ; the stages of growth marked by some- 

 what regular rows of nodes or short spines. 



This species differs from the Z. spinulosa of EDWARDS and HAIME, which it simu- 

 lates principally in the short external spines. The Z. dalii of the same authors, cited 

 as from Warsaw ( Illinois), is probably an associated species, and equally common 

 with the one here described, though not so clearly distinct from a Keokuk species. 



Fig. 1 a. Lateral view of a specimen of medium size. 

 Fig. 1 b. View of the calyx showing the rays. 



Geological formation and locality. In the Warsaw limestone : Warsaw, 

 Illinois. 



