TAXONOMIC RELATIONS OF CHONOPHYLLUM. 277 



some importance. It has been confused more with Omphyma and Ptycho- 

 phyllum than with any other genera; more, however, from external 

 resemblance than from actual similarity in details of structure. We 

 present here the essential characters of these genera and the points by 

 which typical forms of each may be separated from Ohonophyllum. One 

 will not work long, however, before he encounters intermediate forms, 

 the disposition of which will have to depend upon mere individual 

 opinion. These make it all the more necessary that our generic charac- 

 ters be definitely drawn. We do not turn over our land to our neighbor 

 simply because the line fence is down in places. 



Omphyma, Rafinesque and Clifford, 1820. 



The type of this genus is 0. turbinata, Fougt., sp. ; several Gotland 

 specimens of which we have examined along with other foreign and 

 American forms, among which is a series from point. Detour and Drum- 

 monds island, lake Huron, in excellent state of preservation for study. 



The general shape of the corallum and calyx is, as in Chonophyllum, 

 short conical, turbinate, or conico-eylindrical, with basin-like calyx and 

 explanate margins. There seems to be no outer covering which can lie 

 differentiated into a theca and an epitheca, but a single, protective. 

 epithecal covering, showing plainly through it the body structure of the 

 corallum. The best preserved specimens show that it was deposited in 

 exceedingly fine encircling bands or ridges, suggesting the weather- 

 boarding on the side of a frame house. The so-called heavy accretion- 

 ridges of growth do not arise from the epitheca, but from successive con- 

 tractions and expansions of the corallum itself. Likewise the strong and 

 characteristic radiciform processes come from neither epitheca nor wall. 

 but are expansions of the body structures. 



The corallum is made up of a series of superposed cell-cups, which 

 form numerous horizontal tabulae through the central area. The septa 

 are formed by radial infoldings of these continuous cups, sometimes so 

 sharply bent as to form thin septa in the outer area. Usually, however, 

 the septa here are broad and angular, >'. e., show a sharp median ridge 

 giving a roof or tent shape on the upper side. No supporting growths 

 are developed. When viewed in vertical tangential sections these cup- 

 Layers are seen to curve downward through the interseptal cavities, from 

 septum to septum, forming a series of irregular scallops, concave upward 

 through the interseptal cavities, the upturned points marking the posi- 

 tions of the septal ridges. \u radial sections, giving side views of these 

 layers, they are seen to have an additional scalloped structure, now con- 

 vex upward, and forming coarse irregular vesicles. It is thus seen thai 

 thesepta and tlic interseptal cavities are not clearly differentiated ;is in 



\\\ Vll-I'.i i.i. i. n I, So, \„.. \ ,,i . : 1801 



