274 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 105 



Umbonula patens (Smitt) pictured by Osburn (1952, pi. 36, fig. 3) 

 has an imperforate ovicell but other Umbonula species seem to agree 

 with Brown's characterization of the ovicell. No complete, undamaged 

 ovicells were found on U. dentata, so that species still needs clarification 

 on that point. 



Diagnosis: Zooecia encrusting. Frontal an areolate pleuroc37st. 

 Ovicell hyperstomial. Peristome poorly developed. Sometimes an 

 aviculiferous suboral umbo, sometimes avicularia are paired and 

 lateral. Lyrula absent or sometimes simulated by a median frontal 

 process. Orifice large, subcircular to subquadrangular. 



Type species: Hastings (1944), after a detailed study of the litera-'' 

 ture and a careful examination of old museum collections of Umbonula 

 verrucosa (—Cellepora verrucosa Esper 1790), erected Umbonula' 

 omcellata Hastings 1944 as the type species. 



Umbonula dentata (Waters) 



Plate 19 

 Smittia dentata Waters, 1904, p. 71, pi. 4, fig. 8.— Brown, 1952, p. 307. 



Diagnosis: Zooecia encrusting, ovate to hexagonal. Frontal 

 convex, areolated. Orifice large, depressed; with a median variable ( 

 bidentate process. Two small oval avicularia, obliquely placed, one < 

 at each proximal corner of the orifice, have hemispherical mandible 1 

 directed upward and outward. A third similar avicularium some- 

 times on proximal frontal, directed toward nearest orifice (?). Ovicell 

 hyperstomial but no further data on it available at present. 



Measurements: Minimum to maximum and average measurements, 

 in millimeters, are given below (for explanation see p. 271). 



Z-L, 0.807-1.109 (0.929) Ly-L, 0.022-0.058 (0.037) 



Z-W, 0.576-0.634 (0.593) Ly-W, 0.029-0.063 (0.046) 



Av-L, 0.095-0.108 (0.102) Ov-L, 0.288-0.346 (0.320, only four) 



Av-W, 0.072-0.086 (0.081) Ov-W, 0.360-0.432 (0.387, only four) 



Pr-Or-L, 0.187-0.245 (0.216) Op-L, 0.130-0.144 (only 2) 



Pr-Or-W, 0.202-0.230 (0.219) Op-W, 0.187-0.216 (only 2) 



Se-Or-L, 0.216-0.230 (0.219) M-I;, 0.042-0.052 (0.046) 



Se-Or-W, 0.194-0.245 (0.220) M-W, 0.056-0.065 (0.058) 



Zoarium: Zoarium white, encrusting, rather thin-walled. Waters 

 described the species from only one piece, a fragment which lacked 

 ovicells. The U. S. Navy collection material also consisted of one 

 piece of about 20 fairly good zoids growing on another species and 

 only a few broken or incomplete ovicells were present, although on 

 none had the frontal wall become fully formed. 



Zooecia: Zooecia ovate to hexagonal, their vertical walls somewhat 

 curved rather than angular planes. Frontal wall strongly convex, 



