244 PROCEEDINGS OF THE NATIONAL MUSEUM vol. los 



Genotype: Mawsonia membranacea (Thornely, 1924). Type by 

 original designation by Livingstone. 



Mawsonia extensaUtta, new species 



Plates 8,D-F; 9,A-E 



Diagnosis: Colony cylindrical, branching dichotomously. Zooecia 

 arranged in transverse series of 11 to 13 (or possibly more) around 

 the longitudinal axis of the branch with great preciseness so that every 

 other row is in alignment. Cryptocyst closely tubercled and pro- 

 jected outward into two huge wmgs, one on each side of the depressed 

 orifice. These outward projecting wings give the species its name. 

 Orifice longer than wide, curved distally, sides nearly parallel, proximal 

 border very slightly concave. Two very prominent conical proximal 

 condyles borne on a ledge growing from the inner side of the lower lip. 

 Operculum, shaped like the orifice, possesses an inner chitinous flange 

 especially prolonged at the two sides. Ovicells endotoichal, helmet 

 shaped. Avicularia vicarious, as large as autozooecia, and with the 

 pointed beak distally directed. Mandible large, sub triangular, keeled, 

 falciform, and with a median peg projecting from its proximal border. 



Colony: The colony is sturdy and calcareous, branching dichoto- 

 mously. The cylindrical branches are about 24 mm. long and from 

 1.792 to 2.106 mm. (average 2.001 mm.) in diameter. No visible 

 joints occur at the branching but two of the short terminal branches 

 show a slight constriction at the joint. An occasional inconspicuous 

 transverse line, reminiscent of the constrictions found in the genus 

 Cellarinelia but not so wide, so constricted, or so pronounced, occurs 

 along the branches of this species. Although there are variations and 

 masking factors, areolation was more or less hexagonal. The zooecia 

 are regularly arranged in transverse rows of 11 to 13 around the 

 longitudinal axis of the branch (pi. 8,D). These figures, 11 to 13, are 

 from counts made at the ends of two branches. Mathematical calcu- 

 lations show 14 to 15 zoids to be possible in a transverse series else- 

 where along the stalk. The successive transverse rows are placed with 

 such preciseness that the zooecia of every other row (i. e. first and 

 third rows, second and fourth rows, etc.) are in perfect linear alignment 

 with each other, giving the branch the appearance of a very fine file to 

 the unaided eye. The roughness of the surface is due to the huge 

 extended cryptocyst wings which project in pairs from the zooecia 

 (pi. 8,D,E). 



Zooecia: Zooecia are hexagonal in most cases although some are 

 almost square. They are from 0.504 to 0.749 mm. (average 0.652 

 mm.) long, and from 0.346 to 0.562 mm. (average 0.505 mm.) wide. 



