PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 255 



ACTINOZOA. 

 Genus Acervularia, Schweigger. 



Acervularia adjunctiva (sp. uov.). Plato 1, figs. 1, 2, and 3. 



Corallnm massive or subdiscoidal, composed of compactly united 

 eorallites of somewhat unequal size ; coiallites approximately straight, 

 irregularly polygonal, averaging about five millimeters in diameter, 

 their outer surfaces faintly marked by vertical lines which indicate 

 The places of the sej^ta within, but they are not sufficiently distinct to 

 give a crenulated border to the calyx ; these surfaces also present more 

 or less distinct irregular transverse wrinkles or undulations ; outer wall 

 of the eorallites distinct but not thick ; inner wall well developed ; di- 

 ameter of the space inclosed by the inner wall equal to about one-half 

 the tiill diameter of the corallite ; the transverse tabulae of this central 

 space w^ell developed, distinctly separate from each other, their number 

 being about ten to eacli centimeter of length of the corallite. The 

 space between the outer and inner walls is occupied by numerous more 

 or less complete shallow infuudibuliforra plates, which are not quite so 

 numerous as the central tabula?. These plates spring from tlie inner 

 wall, which they successively help to form, and arch ui)ward and outward 

 to the outer wall ; being the successively abandoned floors of the outer 

 portion of the calyces. They appear to have been not always complete, 

 either as regards their extension to the outer wall or their construction 

 of a symmetrical cup, but tliej'^ are apparently no more imperfect in 

 these respects than the calyces of such corals often are. 



The condition of the only specimens discovered is not such as to show 

 any of the calyces in their natural condition, and the structure of the 

 eorallites has therefore been determined by the examination of polished 

 sections, both longitudinal and transverse. While the parts already 

 described are thus distinctly shown, the rays are discovered with dif- 

 ficulty, and they were evidently only slightly developed ; their number, 

 us near as it can be ascertained, is about 16 or 17. 



The geiuis Acervularia has been regarded as peculiarlj' a Devonian 

 form, but as related corals are common to both Devonian and Carbo- 

 niferous strata, there appears no good reason why Acervularia may not 

 exist in the latter. This form seems to differ from the tyjucal species 

 of that genus, at least to such an extent as might be naturally expected 

 of it, when found in strata of so much lat^r date than those which con- 

 tain the typical forms. This is an interesting form, not only as regards 

 its structure, but also in consequence of the marked difference which it 

 presents from any Actinozoan yet described from American Carbonifer- 

 ous strata. 



PoKitioii and locality. — Caboniferous strata, Blackfoot Eange, south of 

 the Yellowstone National Park, where it was discovered hy Prof. O. St. 

 John. 



