32 IOWA ACADEMY OF SCIENCES. 



Acervularia davidsoni, Ed. and H., has a much wider geog:raphical range in Iowa 

 than A. profuiHla, Hall. The area in which A. profunda occurs is nearly all 

 included in part of Buchanan and Black Hawk counties, while the area over whicb 

 the other species is distributed is many times greater. As pointed out in the 

 American Geolof/lst for September, 1891, A. profunda is not associated in the 

 same beds with A. daridsoni, but occurs uniformly at a horizon a few feet lower. 

 Outside the area occupied by A. profunda its place seems to have been taken by 

 PhUlipsaktrea gigas Owen. At least this last species, while never very common, 

 occupies the same relative position a few feet below the horizon at which A~ 

 davidsoni is found, and so far as known it is not present in the region in which A. 

 profunda attains its maximum development. 



With respect to the particulars in which A. profunda diiters from A. davidsoni 

 it agrees essentially in structure with Cgathophi/lhitn rugosum of authors, and it 

 may therefore be regarded as the western i-epresentative of the last named species. 

 If carinated septa have any generic significance, then Cyafhophi;Uum rugosum 

 is not a CgaihophgUum at all. Whatever the decision may be (J. rugosum and J. 

 profunda must ultimately stand side by side in the same genus. 



A. davidsoni stands somewhat apart from both of the foregoing species in a 

 number of particulars. The calyces have a sharply defined central pit with 

 explanate margins. In typical specimens the floor of the calyx, except in the 

 central pit, is almost on a level with the margin; the septa are thick, scarcely 

 denticulated, with but a small portion of their edges free, the carinte are few and 

 clumsy and chiefly developed in the region immediately surrounding the c-mtral 

 area. Both primary and secondary septa are conspicuously thickened around the 

 edge of the central area, the carinte are also developed there better than elsewhere, 

 the effect being to produce in polished sections the appearance of a bi-areal coral 

 with a central area bounded by a definite inner wail. Under the magnifier this 

 wall is never complete. The thickened septa and strongly developed carinse 

 never quite coalesce, so that the outer area is never, as in true bi-areal corals, 

 perfectly shut off" from the central space. At the margin of this central space the 

 secondary septa all end more or less abruptly, and only the primary septa are con- 

 tinued as thin non-carinated lamellae into the central area. 



Acervularia daridsoniis certainly congeneric with some of the species referred 

 to Acervularia by Edwards and Haime and other authors. Whether or not it is 

 generically related to the type species of the genus maybe left an open question. 

 So long as genera are mere artificial creations without sharply defined natural 

 boundaries it will do no violence to the facts, but will be a matter of convenience 

 and at the same time will give effect to a recognizable structural difference, if we 

 keep ^. davidsoni apart from the typical forms of the genus Ci/athophi/Jhon,* 

 and for the present at least retain it in the genus Acervularia. Along with A. 

 davidsoni must go Acervularia inequalis. Hall and Whitfield. As a mere matter 

 of convenience, but with less confidence as to the justness of the arrangement, we 

 may for the present add to the recognized species of Acervularia the A. profunda. 

 Hall, and the CgaihophijUum rugosum of authors. The last two species may yet, 

 with perfect justice, be separated generically from A. davidsoni. 



*Dr. Rominger and Mr. W. J. Davis place this and related species under the genus 

 Cyathovhylhwt. See Geolo.gy of Michigan, Vol. III., and Kenhickij FoksU Corctls. 



