220 BULLETIN 106, UNITED STATES NATIONAL MUSEUM. 



The opesiular indentations serve as a passageway for both the parietal and 

 opercular muscles. Exteriorly the polypiclian convexity quite resembles the poly- 

 pide tube of Steganoporella; but in the interior it is incomplete (pi. 35. fig. 16), 

 and it is rare even that the tuberosities (t) bound it laterally. 



Irregularity is the rule in this genus; all the characters of the opesium are 

 extraordinarily variable. Determination of the species is often difficult and causes 

 much perplexity for the naturalist. 



The opesial processes often join the polypidian convexity, the opesiules thus 

 becoming complete; in the interior the aspect is identical with that of Thalamo- 

 porella. 



The known species of this genus are : 



Floridina (Semicschara) canui Brydone, 1900. 



Floridina (Cellepora) cmstulenta Goldfuss, 1828. 



Floridina (Semieschara) "bimarginata D'Orbigny, 1852. 



Floridina (Mollia) antiqua Smitt, 1873. 



Floridina vendoma Canu, 1900. 



There has as yet been no evidence of the genus in the American Cretaceous. 

 If this observation be confirmed we will be obliged to repeat that the beginning 

 of the Eocene is the time when the change in direction of the Atlantic currents 

 occurred. 



FLORIDINA GEANULOSA, new species. 

 Plate 35, figs. 1-4. 



Description. The zoarium is bilamellar with distorted fronds. The zooecia 

 are distinct, hexagonal, separated by a deep furrow. The mural rim and crypto- 

 cyst are covered with granulations more or less large. The opesium is large, a 

 little elongated, trifoliate; the opesiular portion is large, orbicular and separated 

 from the opercular portion by two salient teeth. The ovicell is endozooecial ; 

 this is a distal convexity little apparent. The onychocellarium is elongated, 

 elliptical, as large as the zooecium ; the opesium is oval, the point above and bears 

 laterally two salient denticles. 



Measurement*. Opesium f^ 0=0.22 mm. . 1 7,2=0.45-0.50 mm. 



,. 'I 7 A 1 r /OOeCia-,, nor n tn 



of zooecia l/o = 0.15 mm. |?= 0.35-0.40 mm. 



Opesium J7i0?i=0.25 mm. . f/,0n=0.45-0.50mm. 



of onychocellariaU07i=0.15 mm. On y chocell: "- umi |7 on =o.35-0.40 mm. 



Variations and affinities. The ovicelled zooecia have an opesium and larger 

 micrometric dimensions (fig. 1). We have observed some calcified zooecia (fig. 2) 

 bearing a lai-ge central perforation. 



This species is very well characterized by the absence (not constant) of the 

 polypidian convexity and by its frontal granulations. 



Occurrence. Lower Jacksonian (Moodys marl) : Jackson. Mississippi (rare). 



Cotypcs.Cat. No. 63980, U.S.N.M. 



