74 L. HILLIS-COLINVAUX 



gigas, which has the largest segments in the genus, length and width 

 data on two segments from living plants, measured a few hours after 

 they were collected from the lagoon of Enewetak Atoll, were 31 x 36 mm 

 and 20 x 36 mm. After drying, these segments measured 21 x 32 mm 

 and 17x30 mm, respectively. Thickness may also be affected, and 

 some segments, particularly those of many discoidea, macroloba and 

 taenicola thalli, become conspicuously concave with drying. The change 

 in all three dimensions is less dramatic with smaller, thinner segments. 



Drying may occasionally collapse the filaments, particularly if 

 segments are lightly calcified. For such specimens, it is very difficult to 

 obtain good measurements from sagittal sections. 



In the species descriptions of this section the principal measure- 

 ments given are for the diameters of the peripheral utricles in surface 

 view (from surface sections), the lengths of the peripheral utricles, the 

 diameters of the secondary utricles and the diameters of the tertiary 

 utricles (from longitudinal sections). For each specimen examined a 

 minimum of ten measurements for each of these characters has been 

 made, and very often more than twice that number, and at times two 

 to several sets of preparations were made for each specimen. The 

 precise number of measurements depends on the species, the reasons for 

 examining it and the quality of the preparations. A good preparation of 

 the surface of the peripheral utricles is usually relatively easy to make, 

 and may have 100 or more utricles, depending on their size and how 

 lavish one is with the specimen. With such a large sample the diameters 

 of utricles were measured randomly, then the field specifically searched 

 for the smallest and largest ones (fusions excepted). 



In sagittal sections, the sample size per section is much more limited 

 because there are many fewer utricles from which to choose initially, 

 and of these some may not be fully expanded or may be damaged. As 

 much as possible, the approach in measuring was the same as for the 

 peripheral utricles. 



For all but a few species the minimum number of measurements 

 obtained for each of the microscopic characters is 100. The average for 

 all species is well over 400, and for some species it is in the thousands. 



The minimum number of nodes dissected for most species is 10, and 

 for many species it is many times this. 



These data provide a spread of measurements which are given in the 

 species descriptions and synopsis (Table X) as the range of measure- 

 ments for the various characters. Figures in parentheses usually 

 represent a few extreme measurements which are included to provide a 

 concept of the range that may be encountered. The narrower range is 

 the one considered representative of the species. 



