PA LA E A CIS 



55 



theca ; tabulae thin ; mural pores indefinitely 

 determined. 



Occurrence. — Locality 12. 



Material. — Specimens studied, 1. Holo- 

 type and only known specimen, University 

 of Michigan No. 23132. 



Remarks. — This specimen may represent 

 a very young corallum of F. divergens 

 White and Whitfield, but this possibility 

 cannot be tested v^ithout study of additional 

 specimens. A label accompanying the speci- 

 men indicates that Girty studied and in- 

 tended to figure it; hov^ever, his findings 

 have not been published and it is not known 

 how he regarded the species. Possibly Girty 

 prepared the polished section figured here. 



Winchell, who did not observe the tabu- 

 lae, thought the species might be referable to 

 Conopoterium, but the regularly disposed 

 corallites are not typical of that genus. 



The specimen is so small that sufficient 

 details cannot be observed to warrant refer- 

 ring it to any genus with certainty, there- 

 fore the writer questionably retains it in 

 its original genus, although it might be re- 

 ferred to F I euro diet yum. 



Genus Pleurodictyum Goldfuss, 1829 



Genotype. — Fleurodictyum problemat- 

 icum Goldfuss, 1829. 



Remarks. — Students are not in agreement 

 as to the proper disposition of Fleurodictyum 

 and Micheliniaj but the writer concurs 

 (Easton, 1943, p. 136) with Lang, Smith, 

 and Thomas (1940, p. 103) that Michelinia 

 is a junior subjective synonym of Fleuro- 

 dictyum. Writers who separate these genera 

 consider Fleurodictyum to be characterized 

 by discoidal or appressed coralla with poly- 

 gonal or subcylindrical corallites radiating 

 from the center of the base and to have the 

 tabulae not markedly arched, septa repre- 

 sented by rows of spines, and irregularly 

 perforate walls. In contrast they consider 

 Michelinid to have larger noticeably angular 

 corallites radiating upward and outward to 

 form rather large coralla with vesicular 

 tabulae. 



Pleurodictyum expansum (White) 



Plate 13, figure 9; Plate 17, figure 2 



Michilinia expansa White, 1880, U. S. Geol. and 

 Geog. Surveys Terr. 12th Ann. Kept., pt. 1; 

 Contr. Invertebrate Paleontology, no. 8, p, 

 158, pi. 39, figs. 2a, b. Advance printing. 



Michilinia expansa, White, 1883, idem. 

 Leptopora typa, Weller, 1898, [in part], U. S. 



Geol. Survey Bull, 153, p. 323. 

 Leptopora expansa, Robinson, 1917, Connecticut 



Acad. Arts Sci. Trans., vol. 21, p. 164. 



Externals. — Corallum conical, gently con- 

 vex on top ; corallites five or six-sided, angles 

 rounded ; calyces very deep, walls vesicular, 

 steep, floor vesicular, tending to be flat; 

 epitheca not preserved. 



Longitudinal section. — Walls very thick, 

 lined with one or two ranges of large vesicles 

 standing nearly vertical; tabulae almost al- 

 ways concave, complete, about 8 in 1 cm. 



Dimensions. — Corallum 2.5 cm high, 5 

 cm by 4 cm across surface ; corallites about 7 

 mm in diameter, 4 or 5 mm deep. 



Occurrence. — Locality 9. 



Material. — Specimens studied, 1. Holo- 

 type and only known specimen. University 

 of Chicago No. 6687. 



Remarks. — Pronounced Liesegang rings 

 in the walls of the single available speci- 

 men, combined with a vugular condition of 

 the vesicles prevent exact determination of 

 the structure, but the species seems distinct 

 from other American representatives of 

 Fleurodictyum. The original description 

 mentions more than one specimen and al- 

 though the one figured was not designated 

 the holotype by White, it is so recorded in 

 the Walker Museum catalogue. 



Appendix to the favositidae 



Remarks. — Falaeacis has been transferred 

 back and forth between the corals and 

 sponges but the genus is now thought to be 

 a possible ally of the Favositidae. Hinde 

 (1896, p. 447) considered it to represent a 

 new family which he did not name. The 

 writer feels that a new family should not be 

 established until a general revision is made. 



Genus Palaeacis Haime in 

 Milne-Edwards, 1857 



Paloeacis Haime, in Milne-Edwards, 1857, His- 

 toire naturelle des coralliaires ou polpyes 

 proprement dits, Atlas, Expl. pi. E-1. 



Palaeacis Haime, in Milne-Edwards, 1860, idem, 

 vol. 3, p. 171. 



Sphenopoterium Meek and Worthen, 1860, Acad. 

 Nat. Sci. Philadelphia Proc, p. 447. 



Ptychochartocyathus Ludwig, 1866, Paleonto- 

 graphica, vol. 14, pt. 5, p. 189. 



Palaeacis, Seebach, 1866, Nachr. Gesellsch. Wis- 

 sensch. zu Gottingen, p. 241. 



