376 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



apertural face; on the other face the zooecia are turned alternately to 

 the right and to the left. 



Genotype. — Retepora elegans Reuss, 1847. Oligocene. 



The genotype is a very rare fossil. The structure appears to us to 

 be rather removed from true Retepora to justify the employment of 

 D'Orbigny's genus. We class it in the second group of Reteporidae 

 (After Waters) awaiting more complete studies. It does not have 

 vibices. 



Family ADEONIDAE Jullien, 1903 



See Canu and Bassler, 1920 and 1923, for descrip- 

 tion of this family and its genera. 



Genus ADEONA (Lamouroux, 1816) Levinsen, 1909 



ADEONA POROSA, new species 



Plate 50, fig. 7 



Description. — The zoarium encrusts nullipores. 

 The zooecia are distinct, separated by a deep fur- 

 row, large, elongated, elliptical, completely sur- 

 rounded by a line of parietal dietellae; the frontal 

 is convex and porous. The apertura is semiellip- 

 tical, transverse and placed at the bottom of a 

 short peristomie. The peristome is smooth, thick, 

 nonsalient. The ascopore is large and placed in 

 the middle of the frontal. The avicularium is 

 located between the ascopore and the apertura; 

 it is large, oblique, triangular, with the point 

 directed upward. 



Measurements. — 



Fig. 143. — Genus 

 Sparsiporina D'Or- 

 bigny, 1851. 



A, B. Sparsipo- 

 rina elegans Reuss, 

 1848. A. Dorsal side 

 with its characteris- 

 tic appearance of the 

 zooecia turned alter- 

 nately to the right 

 and to the left, X 25. 

 B. Frontal side of a 

 branch, X25, show- 

 ing the recumbent 

 ovicell. (After 

 Waters, 1891.) 



. \Jia =0.08 mm. 



A P ertura U.=0.10 



Zooecia 



Lz 



mm. 

 0.50-0.60 mm. 



lz -0.30-0.40 mm. 

 Affinities. — In its dimensions, its aspect and 

 its oblique avicularium, this species resembles 

 Adeona plagiopora Busk, 1859, which Smitt, 

 1872, found in the Gulf of Mexico. It differs from it in its porous 

 frontal and in the absence of tuberosities on the peristome. It has 

 much resemblance to Adeona grisea MacGillivray, 1895, but differs 

 from it in its zoarium, which is encrusting and not bilamellar, 

 fenestrated, and radicellate. 



Only the figured specimen has been found and it is incomplete, 

 but we name the species in order to avoid any confusion with Adeona 

 plagiopora Busk, 1859. 



