Fig. 20. Sagittal sections through an outer portion of about the middle of a Halimeda 

 segment to show different characteristics of the cortical utricles, and of the extent 

 of development of the cortex. A portion of the medulla is included in each. Important 

 characters for the primary utricles are the extent of their lateral attachment, which 

 ranges from about half their length in Nos. 10 and 11 to a thin platform-like edge 

 in Nos. 9 and 12, to none at all in Nos. 1, 8 and sometimes 20; and the number of 

 peripheral utricles supported by each secondary utricle, which ranges from 1, 2 or 4 

 in No. 20 to 14 in No. 11 and 18 in No. 12, but the usual number for most species is 

 2 or 4. (All the utricles supported cannot be shown in a two-dimensional drawing, 

 but the range is apparent.) 



Useful taxonomic characters of the secondary and tertiary (inner) utricles include 

 shape, diameter and length. In diameter, the largest secondary utricles are the 

 bullate ones of discoidea (No. 11). Numbers 12, 9 and 3 are swollen at their peripheral 

 ends. The tertiary utricles of No. 14 are diagnostic, except for some regional speci- 

 mens of discoidea which have a swollen tertiary layer (see text). 



There are two general patterns of development of the cortex. Most species have 



