56 



CHOUTEAU CORALS 



Palacacis, Seebach, 1866, Zeitschr. deutsch. geol. 



Gesellsch., vol. 18, p. 308. 

 Pahwacis, Kunth, 1869, idem, vol. 21, pp. 186, 187. 

 Palacacis, Koninck, 1872, Nouvelles Recherches 



sur les Animaux Fossiles du Terrain Car- 



bonifere de la Belgique, pt. 1, p. 154. 

 Palacacis, Etheridge and Nicholson, 1878, Annals 



and Mag. Nat. History, ser 5, vol. 1, p. 212. 

 Palacacis, Hinde, 1896, Geol. Soc. London Quart. 



Jour., vol. 52, pt. 3, pp. 443-447. 

 Palacacis, Robinson, 1917, Connecticut Acad. Arts 



Sci. Trans., vol. 21, p. 165. 



Diagnosis. — Small, simple to compound 

 corals, calyces shallow, evenly concave, 

 smooth, surface finely reticulate, perforate; 

 septa present in calyces as fine striae ; inter- 

 nal structure reticulate, of anastomosing 

 tubes and vesicles. 



Gejiotype. — Palacacis cuneiforjnis Haime 

 m Milne-Edwards, 1857. 



Occurrence. — Lower Mississippian of 

 United States; Lower Carboniferous (Up- 

 per Visean) of Australia; Lower Carbon- 

 iferous of British Isles. 



Remarks. — Palaeacis is distinguished from 

 Microcyathus chiefly by means of internal 

 structure. The two genera are essentially 

 identical externally, except for the shape of 

 calyces and the mode of attachment of 

 coralla. This genus was first spelled Paloea- 

 cisj an evident misprint which Haime sub- 

 sequently corrected. 



Sphenopoterium Meek and Worthen, 

 1860, has been recognized as a junior syno- 

 nym of Palaeacis since 1866. It was founded 

 upon S. obtusum Meek and Worthen from 

 Keokuk beds near Nauvoo, Illinois. 



Conopoterium Winchell, 1865, was 

 founded upon C. effusum Winchell. 

 Etheridge and Nicholson (1878, p. 217) 

 believed this genus to be a relative of 

 Palaeacis but a study of the types of C. 

 ejfusujn shows that it is quite unlike Palaea- 

 cis, being more closely allied to typical 

 Favositidae. Conopterium (Keyes, 1894, p. 

 118 and Weller, 1898, p. 189) is a mis- 

 spelling. 



Ptychochartocyathus Ludwig, 1866, is a 

 junior synonym of Palaeacis, but is rarelv 

 found in the literature because most authors 

 have ignored Ludwig's genera. Lang and 

 Smith have applied to the International 

 Commission on Zoological Nomenclature 

 for suppression of all Ludwig's genera on 



the grounds of unnecessary complexity and 

 faulty foundation. The decision is pending. 



For a review of the early opinions regard- 

 ing Palaeacis, its synonyms, and its relation- 

 ships, see Etheridge and Nicholson (1878). 

 They considered only three species to be 

 available and believed P. enorme to be a 

 junior synonym of P. cyclostoma (Phillips). 

 Lack of comparative material prevents the 

 writer from attempting to evaluate their 

 conclusions and he prefers to recognize 

 species of Palaeacis on the basis of symmetry, 

 shape, and number of corallites. 



Palaeacis enorinis var. depressus Meek 

 and Worthen is erroneously listed from the 

 Rockford limestone in Indiana by Etheridge 

 and Nicholson (1878, p. 225). This variety 

 is known only from the Fern Glen forma- 

 tion of Illinois. It and the two preceding 

 species are actually referable to Micro- 

 cyathus. 



Palaeacis conica Easton, n. sp. 



Plate 16, figure 19 



Zaphrentis tantilla Miller, 1891, [in part], In- 

 diana Dept. Geol. Nat. Res., 17th Ann. Rept., 

 p. 11. Adv. Sheets. 



Zaphrentis tantilla. Miller, 1892, [in part], In- 

 diana Dept. Geol. Nat. Res., 17th Ann. Rept., 

 pp. 621, 622. 



Description. — Corallum ceratoid, ellipti- 

 cal in cross-section, very slightly curved ; 

 exterior covered with fine anastomosing fur- 

 rows ; small secondary corraHte extends 

 short distance from primary calyx; calyx 

 moderately deep, evenly concave, without 

 evidence of calical structures. Height 12.0 

 mm, greatest diameter 4.2 mm, least di- 

 ameter in same plane 3.8 mm. 



Comparison. — This species differs from 

 P. bifidus Weller from the Fern Glen for- 

 mation in being curved ceratoid, not ex- 

 tremely flattened, and in having only one 

 small subordinate offset. 



Occurrence. — Localities 7, 8. 



Material. — Specimens studied, 2. Holo- 

 type. University of Cincinnati No. 24310; 

 possible representative, University of Chi- 

 cago No. 9767. 



Remarks. — The holotype was formerly 

 one of the cotypes of Z. tantilla Miller and 

 as such was only partially freed of its 

 matrix. It is so very different from other 

 described Palaeacis that it warrants separate 

 recognition. 



