INVERTEBRATES. 417 



shallow dimples seem to have denuded the surface. These 

 scars are somewhat irregular in form and distribution, but are 

 mostly oblong-oval in shape. This is no doubt a beautiful 

 species, but the specimen from which the description is drawn 

 is too small and imperfect to give a full view of all its characters. 



Geological position and locality: Keokuk group, Warsaw, Illinois. 



Genus CYCLOPORA, Prout. 



Cyclopora, Prout, 1860. Proceedings of St. Louis Academy of Science, vol. i, p. 574. 



Polyzoum discoidal, frondescent, or irregularly incrusting; 

 plates sometimes superposed, with subprismatic chalices longer 

 than broad, having their sides formed of a minutely porous inter- 

 stitial net-work, developed from a sole marked by transverse 

 bands or wrinkles more or less concentric, sometimes intercur- 

 rent or contorted, which are crossed at right angles by delicate, 

 slightly interrupted lines, separating the bases of the chalices 

 and radiating to an actual or imaginary centre almost as regu- 

 larly as the hymenium of a mushroom or the plates of a Fungia, 

 without being, like these, entire in their vertical expansion ; 

 chalice apertures on one or both faces shallow and expanded, 

 with interstitial spaces porous and net-like. 



We have been induced, from the considerations which follow, to separate 

 this genus from the Ceriopora of Goldfuss. This genus, as defined by its 

 author, was rendered too comprehensive, and embraced within its limits too 

 large an assemblage of heterogeneous forms. Many of these have been 

 transferred by subsequent writers to other genera; and M. deOrbigny has 

 more recently excluded from its limits all expansive or incrusting forms, 

 restricting it to such as are ramose, having one or more layers of cells 

 superimposed upon one another, which includes in part the Inversaria of 

 Hagenow. We do not feel disposed to admit this mere modification in the 

 growth of the polyzoum, taken separately and alone, as an adequate basis for 

 generic distinction ; for it is well known that the superposition of layer upon 

 layer may be the result of age, and we have observed several times, in our in- 



— 53 Oot. 5, 1S06. 



