318 



BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



We are able to distinguish the principal genera only by the nature of their 

 frontal. 



Following the Membraniporae, these are the most ancient Cheilostome fossils 

 known. 



Genus ACROPORA Reuss, 1869. 



1S69. Acropora RETJSS, Die fossilen Anthozoen und Bryozoen der Schichtengruppe von 

 Crosaro, Denkschriften der k. Akademie der Wissenschaften, Wien, vol. 29, p. 277. 



The zoarium is free and escharian. The frontal is a thick tremocyst with 

 tubules. The avicularia are grouped on the peristome. 



Genotypes. Acropora (Eschara) gracilis Milne Edwards, 1836, of the Aus- 

 tralian seas and Acropora (Cellaria) coronata Eeuss, 1847, a fossil of the Vicentin. 



Range. Jacksonian-Recent. 



A. Acropora. B. Gastropella. C. Pachytheca. D. Beisselina. 



FIG. 89. Genera of the family Acroporidae Canu, 1913. 



A. Acropora saillans, new species, X 20. Vieksburgian, 1 mile north of Mouroeville. Alabama. 



B. Gastropella ventricosa Cnnn and Bassler, 1917, X 20. Midwayan of Arkansas. 



C. Pachytheca stipata, new species, X20, Midwayan, Crenshaw County, Alabama. 



D. Beisselina trulla, new species, X 20. Lower Jacksonian. Jackson, Mississippi. 



The known species of this genus are: 



Acropora (Eschara) coronata Von Hagenow, 1851 (not Reuss). Maestrichtian. 



Acropora (Cellaria) coronata Reuss, 1847. Priabonian. 



Acropora (Entalophora) gmteloupi D'Orbigny, 1851. Lutetian. 



Acropora (Porina) contorta Canu. 1910. Auversian. 



Acropora (Pustultpora) mamillata D'Archiac, 1846. Auversian. 



Acropora (Eschara) gracilis Milne Edwards, 1836. Recent. 



ACROPORA TRITA, new species. 



Plate 6, figs. 5, 6. 



Description. The zoarium is free, cylindrical, bifurcated. The zooecia are 

 indistinct ; their frontal is confused with the zoarial surface and it is formed of a 

 tremocyst with small scattered pores. It has no salient peristomes. The peristomice 

 is oblique, elliptical, transverse. 



. \hpeQ.Wmm. 



Measurements. Jreristomice \ , _ 1 _ 



(lpe=0.1o mm. 



