INVERTEBRATES. 419 



having full faith that principles grounded in nature, fully comprehended and 

 properly interpreted, cannot very far mislead the earnest and humble inquirer 

 after truth. We hope, by our labors, to remove some of the difficulties which 

 oppose themselves to a better understanding of the zoological and palaeontologi- 

 cal value of this beautiful and interesting, but hitherto much neglected order 

 of fossil forms. 



The genus established above is one which embraces several discoidal and 

 incrusting forms. The concentric, more or less banded basis or sole which 

 from its thickening into folds or ridges, gives more strength and firmness to 

 the net-work in which the tiny workers above were implanted, sufficiently dis- 

 tinguishes it from the Semieoscinium, with its more or less lamellar and con- 

 densed intercellular spaces, and its sole condensed in parallel ridges; from 

 Coscinium, with its raised chalice lips, and its sole formed of approximating and 

 receding ridges; or from Cheetetes, with its more condensed intercellular spaces 

 and its longer tubes, which take their origin in an uncondensed cellular or 

 cancellous structure. The basis of its separation from its congeners of the 

 same group is founded mainly upon the form and character of its sole. This 

 banded arrangement of the condensed base seems to be represented in Ceriopora 

 verrucosa, Gold., tab. x, fig. 6c, which most probably belongs to this genus. 

 Now, it may be said that where the general characters and the arrangement of 

 the chalices are nearly the same, the distinctions in the form of the sole possess 

 little or no generic value; but this objection can have but little force, unless it 

 can be proved that these differences in the character of the basal plates, and 

 the direction and distribution of the chalices which impressed these forms upon 

 them, were accidental, and not strictly the result of differences in the laws 

 which regulate the definite development of organic forms. 



Cyclopora fungia, Prout. 



PI. 22, fig. 9, da, 9 5. 

 Cyclopora fungia, Prout, 1860. Proceed. St. Louis Acad. Sci., vol. 1, p. 577. 



Polyzoum a flattened disc, about two inches in diameter, 

 with a central depression on the lower surface, and a some- 

 what irregular margin ; strise or sole-lines radiating from the 

 centre, somewhat whorled at first, delicate, interrupted or 

 jagged, being apparently formed of long, slightly waved, sep- 

 tate, flattened tubes, in juxtaposition on a common plane of 

 expansion ; concentric rings more or less rugosel y plicated, and 



